Internet DRAFT - draft-melnikov-rfc3501bis
draft-melnikov-rfc3501bis
Network Working Group A. Melnikov, Ed.
Internet-Draft Isode Ltd
Obsoletes: 3501 (if approved) October 18, 2015
Intended status: Standards Track
Expires: April 20, 2016
INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1
draft-melnikov-rfc3501bis-05.txt
Abstract
The Internet Message Access Protocol, Version 4rev1 (IMAP4rev1)
allows a client to access and manipulate electronic mail messages on
a server. IMAP4rev1 permits manipulation of mailboxes (remote
message folders) in a way that is functionally equivalent to local
folders. IMAP4rev1 also provides the capability for an offline
client to resynchronize with the server.
IMAP4rev1 includes operations for creating, deleting, and renaming
mailboxes, checking for new messages, permanently removing messages,
setting and clearing flags, RFC 5322 and RFC 2045 parsing, searching,
and selective fetching of message attributes, texts, and portions
thereof. Messages in IMAP4rev1 are accessed by the use of numbers.
These numbers are either message sequence numbers or unique
identifiers.
IMAP4rev1 supports a single server. A mechanism for accessing
configuration information to support multiple IMAP4rev1 servers is
discussed in RFC 2244.
IMAP4rev1 does not specify a means of posting mail; this function is
handled by a mail transfer protocol such as RFC 5321.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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This Internet-Draft will expire on April 20, 2016.
Copyright Notice
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Table of Contents
1. How to Read This Document . . . . . . . . . . . . . . . . . . 4
1.1. Organization of This Document . . . . . . . . . . . . . . 5
1.2. Conventions Used in This Document . . . . . . . . . . . . 5
1.3. Special Notes to Implementors . . . . . . . . . . . . . . 6
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Link Level . . . . . . . . . . . . . . . . . . . . . . . 6
2.2. Commands and Responses . . . . . . . . . . . . . . . . . 7
2.2.1. Client Protocol Sender and Server Protocol Receiver . 7
2.2.2. Server Protocol Sender and Client Protocol Receiver . 8
2.3. Message Attributes . . . . . . . . . . . . . . . . . . . 8
2.3.1. Message Numbers . . . . . . . . . . . . . . . . . . . 9
2.3.2. Flags Message Attribute . . . . . . . . . . . . . . . 11
2.3.3. Internal Date Message Attribute . . . . . . . . . . . 12
2.3.4. [RFC-5322] Size Message Attribute . . . . . . . . . . 12
2.3.5. Envelope Structure Message Attribute . . . . . . . . 12
2.3.6. Body Structure Message Attribute . . . . . . . . . . 13
2.4. Message Texts . . . . . . . . . . . . . . . . . . . . . . 13
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3. State and Flow Diagram . . . . . . . . . . . . . . . . . . . 13
3.1. Not Authenticated State . . . . . . . . . . . . . . . . . 13
3.2. Authenticated State . . . . . . . . . . . . . . . . . . . 13
3.3. Selected State . . . . . . . . . . . . . . . . . . . . . 13
3.4. Logout State . . . . . . . . . . . . . . . . . . . . . . 14
4. Data Formats . . . . . . . . . . . . . . . . . . . . . . . . 15
4.1. Atom . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.2. Number . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.3. String . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.3.1. 8-bit and Binary Strings . . . . . . . . . . . . . . 16
4.4. Parenthesized List . . . . . . . . . . . . . . . . . . . 17
4.5. NIL . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5. Operational Considerations . . . . . . . . . . . . . . . . . 17
5.1. Mailbox Naming . . . . . . . . . . . . . . . . . . . . . 17
5.1.1. Mailbox Hierarchy Naming . . . . . . . . . . . . . . 18
5.1.2. Mailbox Namespace Naming Convention . . . . . . . . . 18
5.1.3. Mailbox International Naming Convention . . . . . . . 19
5.2. Mailbox Size and Message Status Updates . . . . . . . . . 20
5.3. Response when no Command in Progress . . . . . . . . . . 21
5.4. Autologout Timer . . . . . . . . . . . . . . . . . . . . 21
5.5. Multiple Commands in Progress . . . . . . . . . . . . . . 21
6. Client Commands . . . . . . . . . . . . . . . . . . . . . . . 22
6.1. Client Commands - Any State . . . . . . . . . . . . . . . 23
6.1.1. CAPABILITY Command . . . . . . . . . . . . . . . . . 23
6.1.2. NOOP Command . . . . . . . . . . . . . . . . . . . . 24
6.1.3. LOGOUT Command . . . . . . . . . . . . . . . . . . . 25
6.2. Client Commands - Not Authenticated State . . . . . . . . 25
6.2.1. STARTTLS Command . . . . . . . . . . . . . . . . . . 26
6.2.2. AUTHENTICATE Command . . . . . . . . . . . . . . . . 27
6.2.3. LOGIN Command . . . . . . . . . . . . . . . . . . . . 29
6.3. Client Commands - Authenticated State . . . . . . . . . . 30
6.3.1. SELECT Command . . . . . . . . . . . . . . . . . . . 30
6.3.2. EXAMINE Command . . . . . . . . . . . . . . . . . . . 32
6.3.3. CREATE Command . . . . . . . . . . . . . . . . . . . 33
6.3.4. DELETE Command . . . . . . . . . . . . . . . . . . . 34
6.3.5. RENAME Command . . . . . . . . . . . . . . . . . . . 35
6.3.6. SUBSCRIBE Command . . . . . . . . . . . . . . . . . . 37
6.3.7. UNSUBSCRIBE Command . . . . . . . . . . . . . . . . . 38
6.3.8. LIST Command . . . . . . . . . . . . . . . . . . . . 38
6.3.9. LSUB Command . . . . . . . . . . . . . . . . . . . . 41
6.3.10. STATUS Command . . . . . . . . . . . . . . . . . . . 42
6.3.11. APPEND Command . . . . . . . . . . . . . . . . . . . 43
6.4. Client Commands - Selected State . . . . . . . . . . . . 45
6.4.1. CHECK Command . . . . . . . . . . . . . . . . . . . . 45
6.4.2. CLOSE Command . . . . . . . . . . . . . . . . . . . . 45
6.4.3. EXPUNGE Command . . . . . . . . . . . . . . . . . . . 46
6.4.4. SEARCH Command . . . . . . . . . . . . . . . . . . . 47
6.4.5. FETCH Command . . . . . . . . . . . . . . . . . . . . 50
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6.4.6. STORE Command . . . . . . . . . . . . . . . . . . . . 54
6.4.7. COPY Command . . . . . . . . . . . . . . . . . . . . 55
6.4.8. UID Command . . . . . . . . . . . . . . . . . . . . . 56
6.5. Client Commands - Experimental/Expansion . . . . . . . . 57
6.5.1. X<atom> Command . . . . . . . . . . . . . . . . . . . 57
7. Server Responses . . . . . . . . . . . . . . . . . . . . . . 58
7.1. Server Responses - Status Responses . . . . . . . . . . . 59
7.1.1. OK Response . . . . . . . . . . . . . . . . . . . . . 60
7.1.2. NO Response . . . . . . . . . . . . . . . . . . . . . 61
7.1.3. BAD Response . . . . . . . . . . . . . . . . . . . . 61
7.1.4. PREAUTH Response . . . . . . . . . . . . . . . . . . 61
7.1.5. BYE Response . . . . . . . . . . . . . . . . . . . . 62
7.2. Server Responses - Server and Mailbox Status . . . . . . 62
7.2.1. CAPABILITY Response . . . . . . . . . . . . . . . . . 63
7.2.2. LIST Response . . . . . . . . . . . . . . . . . . . . 64
7.2.3. LSUB Response . . . . . . . . . . . . . . . . . . . . 65
7.2.4. STATUS Response . . . . . . . . . . . . . . . . . . . 65
7.2.5. SEARCH Response . . . . . . . . . . . . . . . . . . . 65
7.2.6. FLAGS Response . . . . . . . . . . . . . . . . . . . 65
7.3. Server Responses - Mailbox Size . . . . . . . . . . . . . 66
7.3.1. EXISTS Response . . . . . . . . . . . . . . . . . . . 66
7.3.2. RECENT Response . . . . . . . . . . . . . . . . . . . 66
7.4. Server Responses - Message Status . . . . . . . . . . . . 67
7.4.1. EXPUNGE Response . . . . . . . . . . . . . . . . . . 67
7.4.2. FETCH Response . . . . . . . . . . . . . . . . . . . 68
7.5. Server Responses - Command Continuation Request . . . . . 73
8. Sample IMAP4rev1 connection . . . . . . . . . . . . . . . . . 73
9. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 75
10. Author's Note . . . . . . . . . . . . . . . . . . . . . . . . 85
11. Security Considerations . . . . . . . . . . . . . . . . . . . 85
11.1. STARTTLS Security Considerations . . . . . . . . . . . . 86
11.2. Other Security Considerations . . . . . . . . . . . . . 86
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 87
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 87
13.1. Normative References . . . . . . . . . . . . . . . . . . 88
13.2. Informative References (related protocols) . . . . . . . 89
13.3. Informative References (historical aspects of IMAP and
related protocols) . . . . . . . . . . . . . . . . . . . 90
Appendix A. Changes from RFC 3501 . . . . . . . . . . . . . . . 91
Appendix B. Acknowledgement . . . . . . . . . . . . . . . . . . 91
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 95
1. How to Read This Document
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1.1. Organization of This Document
This document is written from the point of view of the implementor of
an IMAP4rev1 client or server. Beyond the protocol overview in
section 2, it is not optimized for someone trying to understand the
operation of the protocol. The material in sections 3 through 5
provides the general context and definitions with which IMAP4rev1
operates.
Sections 6, 7, and 9 describe the IMAP commands, responses, and
syntax, respectively. The relationships among these are such that it
is almost impossible to understand any of them separately. In
particular, do not attempt to deduce command syntax from the command
section alone; instead refer to the Formal Syntax section.
1.2. Conventions Used in This Document
"Conventions" are basic principles or procedures. Document
conventions are noted in this section.
In examples, "C:" and "S:" indicate lines sent by the client and
server respectively.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [KEYWORDS].
The word "can" (not "may") is used to refer to a possible
circumstance or situation, as opposed to an optional facility of the
protocol.
"User" is used to refer to a human user, whereas "client" refers to
the software being run by the user.
"Connection" refers to the entire sequence of client/server
interaction from the initial establishment of the network connection
until its termination.
"Session" refers to the sequence of client/server interaction from
the time that a mailbox is selected (SELECT or EXAMINE command) until
the time that selection ends (SELECT or EXAMINE of another mailbox,
CLOSE command, or connection termination).
Characters are 7-bit US-ASCII unless otherwise specified. Other
character sets are indicated using a "CHARSET", as described in
[MIME-IMT] and defined in [CHARSET]. CHARSETs have important
additional semantics in addition to defining character set; refer to
these documents for more detail.
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There are several protocol conventions in IMAP. These refer to
aspects of the specification which are not strictly part of the IMAP
protocol, but reflect generally-accepted practice. Implementations
need to be aware of these conventions, and avoid conflicts whether or
not they implement the convention. For example, "&" may not be used
as a hierarchy delimiter since it conflicts with the Mailbox
International Naming Convention, and other uses of "&" in mailbox
names are impacted as well.
1.3. Special Notes to Implementors
Implementors of the IMAP protocol are strongly encouraged to read the
IMAP implementation recommendations document [IMAP-IMPLEMENTATION] in
conjunction with this document, to help understand the intricacies of
this protocol and how best to build an interoperable product.
IMAP4rev1 is designed to be upwards compatible from the [IMAP2] and
unpublished IMAP2bis protocols. IMAP4rev1 is largely compatible with
the IMAP4 protocol described in RFC 1730; the exception being in
certain facilities added in RFC 1730 that proved problematic and were
subsequently removed. In the course of the evolution of IMAP4rev1,
some aspects in the earlier protocols have become obsolete. Obsolete
commands, responses, and data formats which an IMAP4rev1
implementation can encounter when used with an earlier implementation
are described in [IMAP-OBSOLETE].
Other compatibility issues with IMAP2bis, the most common variant of
the earlier protocol, are discussed in [IMAP-COMPAT]. A full
discussion of compatibility issues with rare (and presumed extinct)
variants of [IMAP2] is in [IMAP-HISTORICAL]; this document is
primarily of historical interest.
IMAP was originally developed for the older [RFC-822] standard, and
as a consequence several fetch items in IMAP incorporate "RFC822" in
their name. With the exception of RFC822.SIZE, there are more modern
replacements; for example, the modern version of RFC822.HEADER is
BODY.PEEK[HEADER]. In all cases, "RFC822" should be interpreted as a
reference to the updated [RFC-5322] standard.
2. Protocol Overview
2.1. Link Level
The IMAP4rev1 protocol assumes a reliable data stream such as that
provided by TCP. When TCP is used, an IMAP4rev1 server listens on
port 143.
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2.2. Commands and Responses
An IMAP4rev1 connection consists of the establishment of a client/
server network connection, an initial greeting from the server, and
client/server interactions. These client/server interactions consist
of a client command, server data, and a server completion result
response.
All interactions transmitted by client and server are in the form of
lines, that is, strings that end with a CRLF. The protocol receiver
of an IMAP4rev1 client or server is either reading a line, or is
reading a sequence of octets with a known count followed by a line.
2.2.1. Client Protocol Sender and Server Protocol Receiver
The client command begins an operation. Each client command is
prefixed with an identifier (typically a short alphanumeric string,
e.g., A0001, A0002, etc.) called a "tag". A different tag is
generated by the client for each command.
Clients MUST follow the syntax outlined in this specification
strictly. It is a syntax error to send a command with missing or
extraneous spaces or arguments.
There are two cases in which a line from the client does not
represent a complete command. In one case, a command argument is
quoted with an octet count (see the description of literal in String
under Data Formats); in the other case, the command arguments require
server feedback (see the AUTHENTICATE command). In either case, the
server sends a command continuation request response if it is ready
for the octets (if appropriate) and the remainder of the command.
This response is prefixed with the token "+".
Note: If instead, the server detected an error in the command, it
sends a BAD completion response with a tag matching the command
(as described below) to reject the command and prevent the client
from sending any more of the command.
It is also possible for the server to send a completion response
for some other command (if multiple commands are in progress), or
untagged data. In either case, the command continuation request
is still pending; the client takes the appropriate action for the
response, and reads another response from the server. In all
cases, the client MUST send a complete command (including
receiving all command continuation request responses and command
continuations for the command) before initiating a new command.
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The protocol receiver of an IMAP4rev1 server reads a command line
from the client, parses the command and its arguments, and transmits
server data and a server command completion result response.
2.2.2. Server Protocol Sender and Client Protocol Receiver
Data transmitted by the server to the client and status responses
that do not indicate command completion are prefixed with the token
"*", and are called untagged responses.
Server data MAY be sent as a result of a client command, or MAY be
sent unilaterally by the server. There is no syntactic difference
between server data that resulted from a specific command and server
data that were sent unilaterally.
The server completion result response indicates the success or
failure of the operation. It is tagged with the same tag as the
client command which began the operation. Thus, if more than one
command is in progress, the tag in a server completion response
identifies the command to which the response applies. There are
three possible server completion responses: OK (indicating success),
NO (indicating failure), or BAD (indicating a protocol error such as
unrecognized command or command syntax error).
Servers SHOULD enforce the syntax outlined in this specification
strictly. Any client command with a protocol syntax error, including
(but not limited to) missing or extraneous spaces or arguments,
SHOULD be rejected, and the client given a BAD server completion
response.
The protocol receiver of an IMAP4rev1 client reads a response line
from the server. It then takes action on the response based upon the
first token of the response, which can be a tag, a "*", or a "+".
A client MUST be prepared to accept any server response at all times.
This includes server data that was not requested. Server data SHOULD
be recorded, so that the client can reference its recorded copy
rather than sending a command to the server to request the data. In
the case of certain server data, the data MUST be recorded.
This topic is discussed in greater detail in the Server Responses
section.
2.3. Message Attributes
In addition to message text, each message has several attributes
associated with it. These attributes can be retrieved individually
or in conjunction with other attributes or message texts.
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2.3.1. Message Numbers
Messages in IMAP4rev1 are accessed by one of two numbers; the unique
identifier or the message sequence number.
2.3.1.1. Unique Identifier (UID) Message Attribute
An unsigned 32-bit value assigned to each message, which when used
with the unique identifier validity value (see below) forms a 64-bit
value that MUST NOT refer to any other message in the mailbox or any
subsequent mailbox with the same name forever. Unique identifiers
are assigned in a strictly ascending fashion in the mailbox; as each
message is added to the mailbox it is assigned a higher UID than the
message(s) which were added previously. Unlike message sequence
numbers, unique identifiers are not necessarily contiguous.
The unique identifier of a message MUST NOT change during the
session, and SHOULD NOT change between sessions. Any change of
unique identifiers between sessions MUST be detectable using the
UIDVALIDITY mechanism discussed below. Persistent unique identifiers
are required for a client to resynchronize its state from a previous
session with the server (e.g., disconnected or offline access
clients); this is discussed further in [IMAP-DISC].
Associated with every mailbox are two 32-bit unsigned values which
aid in unique identifier handling: the next unique identifier value
(UIDNEXT) and the unique identifier validity value (UIDVALIDITY).
The next unique identifier value is the predicted value that will be
assigned to a new message in the mailbox. Unless the unique
identifier validity also changes (see below), the next unique
identifier value MUST have the following two characteristics. First,
the next unique identifier value MUST NOT change unless new messages
are added to the mailbox; and second, the next unique identifier
value MUST change whenever new messages are added to the mailbox,
even if those new messages are subsequently expunged.
Note: The next unique identifier value is intended to provide a
means for a client to determine whether any messages have been
delivered to the mailbox since the previous time it checked this
value. It is not intended to provide any guarantee that any
message will have this unique identifier. A client can only
assume, at the time that it obtains the next unique identifier
value, that messages arriving after that time will have a UID
greater than or equal to that value.
The unique identifier validity value is sent in a UIDVALIDITY
response code in an OK untagged response at mailbox selection time.
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If unique identifiers from an earlier session fail to persist in this
session, the unique identifier validity value MUST be greater than
the one used in the earlier session.
Note: Ideally, unique identifiers SHOULD persist at all times.
Although this specification recognizes that failure to persist can
be unavoidable in certain server environments, it STRONGLY
ENCOURAGES message store implementation techniques that avoid this
problem. For example:
1. Unique identifiers MUST be strictly ascending in the mailbox
at all times. If the physical message store is re-ordered by
a non-IMAP agent, this requires that the unique identifiers in
the mailbox be regenerated, since the former unique
identifiers are no longer strictly ascending as a result of
the re-ordering.
2. If the message store has no mechanism to store unique
identifiers, it must regenerate unique identifiers at each
session, and each session must have a unique UIDVALIDITY
value.
3. If the mailbox is deleted and a new mailbox with the same name
is created at a later date, the server must either keep track
of unique identifiers from the previous instance of the
mailbox, or it must assign a new UIDVALIDITY value to the new
instance of the mailbox. A good UIDVALIDITY value to use in
this case is a 32-bit representation of the creation date/time
of the mailbox. It is alright to use a constant such as 1,
but only if it guaranteed that unique identifiers will never
be reused, even in the case of a mailbox being deleted (or
renamed) and a new mailbox by the same name created at some
future time.
4. The combination of mailbox name, UIDVALIDITY, and UID must
refer to a single immutable message on that server forever.
In particular, the internal date, [RFC-5322] size, envelope,
body structure, and message texts (RFC822, RFC822.HEADER,
RFC822.TEXT, and all BODY[...] fetch data items) must never
change. This does not include message numbers, nor does it
include attributes that can be set by a STORE command (e.g.,
FLAGS).
2.3.1.2. Message Sequence Number Message Attribute
A relative position from 1 to the number of messages in the mailbox.
This position MUST be ordered by ascending unique identifier. As
each new message is added, it is assigned a message sequence number
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that is 1 higher than the number of messages in the mailbox before
that new message was added.
Message sequence numbers can be reassigned during the session. For
example, when a message is permanently removed (expunged) from the
mailbox, the message sequence number for all subsequent messages is
decremented. The number of messages in the mailbox is also
decremented. Similarly, a new message can be assigned a message
sequence number that was once held by some other message prior to an
expunge.
In addition to accessing messages by relative position in the
mailbox, message sequence numbers can be used in mathematical
calculations. For example, if an untagged "11 EXISTS" is received,
and previously an untagged "8 EXISTS" was received, three new
messages have arrived with message sequence numbers of 9, 10, and 11.
Another example, if message 287 in a 523 message mailbox has UID
12345, there are exactly 286 messages which have lesser UIDs and 236
messages which have greater UIDs.
2.3.2. Flags Message Attribute
A list of zero or more named tokens associated with the message. A
flag is set by its addition to this list, and is cleared by its
removal. There are two types of flags in IMAP4rev1. A flag of
either type can be permanent or session-only.
A system flag is a flag name that is pre-defined in this
specification. All system flags begin with "\". Certain system
flags (\Deleted and \Seen) have special semantics described
elsewhere. The currently-defined system flags are:
\Seen Message has been read
\Answered Message has been answered
\Flagged Message is "flagged" for urgent/special attention
\Deleted Message is "deleted" for removal by later EXPUNGE
\Draft Message has not completed composition (marked as a draft).
\Recent Message is "recently" arrived in this mailbox. This session
is the first session to have been notified about this message; if
the session is read-write, subsequent sessions will not see
\Recent set for this message. This flag can not be altered by the
client.
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If it is not possible to determine whether or not this session is
the first session to be notified about a message, then that
message SHOULD be considered recent.
If multiple connections have the same mailbox selected
simultaneously, it is undefined which of these connections will
see newly-arrived messages with \Recent set and which will see it
without \Recent set.
A keyword is defined by the server implementation. Keywords do not
begin with "\". Servers MAY permit the client to define new keywords
in the mailbox (see the description of the PERMANENTFLAGS response
code for more information).
A flag can be permanent or session-only on a per-flag basis.
Permanent flags are those which the client can add or remove from the
message flags permanently; that is, concurrent and subsequent
sessions will see any change in permanent flags. Changes to session
flags are valid only in that session.
Note: The \Recent system flag is a special case of a session flag.
\Recent can not be used as an argument in a STORE or APPEND
command, and thus can not be changed at all.
2.3.3. Internal Date Message Attribute
The internal date and time of the message on the server. This is not
the date and time in the [RFC-5322] header, but rather a date and
time which reflects when the message was received. In the case of
messages delivered via [SMTP], this SHOULD be the date and time of
final delivery of the message as defined by [SMTP]. In the case of
messages delivered by the IMAP4rev1 COPY command, this SHOULD be the
internal date and time of the source message. In the case of
messages delivered by the IMAP4rev1 APPEND command, this SHOULD be
the date and time as specified in the APPEND command description.
All other cases are implementation defined.
2.3.4. [RFC-5322] Size Message Attribute
The number of octets in the message, as expressed in [RFC-5322]
format.
2.3.5. Envelope Structure Message Attribute
A parsed representation of the [RFC-5322] header of the message.
Note that the IMAP Envelope structure is not the same as an [SMTP]
envelope.
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2.3.6. Body Structure Message Attribute
A parsed representation of the [MIME-IMB] body structure information
of the message.
2.4. Message Texts
In addition to being able to fetch the full [RFC-5322] text of a
message, IMAP4rev1 permits the fetching of portions of the full
message text. Specifically, it is possible to fetch the [RFC-5322]
message header, [RFC-5322] message body, a [MIME-IMB] body part, or a
[MIME-IMB] header.
3. State and Flow Diagram
Once the connection between client and server is established, an
IMAP4rev1 connection is in one of four states. The initial state is
identified in the server greeting. Most commands are only valid in
certain states. It is a protocol error for the client to attempt a
command while the connection is in an inappropriate state, and the
server will respond with a BAD or NO (depending upon server
implementation) command completion result.
3.1. Not Authenticated State
In the not authenticated state, the client MUST supply authentication
credentials before most commands will be permitted. This state is
entered when a connection starts unless the connection has been pre-
authenticated.
3.2. Authenticated State
In the authenticated state, the client is authenticated and MUST
select a mailbox to access before commands that affect messages will
be permitted. This state is entered when a pre-authenticated
connection starts, when acceptable authentication credentials have
been provided, after an error in selecting a mailbox, or after a
successful CLOSE command.
3.3. Selected State
In a selected state, a mailbox has been selected to access. This
state is entered when a mailbox has been successfully selected.
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3.4. Logout State
In the logout state, the connection is being terminated. This state
can be entered as a result of a client request (via the LOGOUT
command) or by unilateral action on the part of either the client or
server.
If the client requests the logout state, the server MUST send an
untagged BYE response and a tagged OK response to the LOGOUT command
before the server closes the connection; and the client MUST read the
tagged OK response to the LOGOUT command before the client closes the
connection.
A server MUST NOT unilaterally close the connection without sending
an untagged BYE response that contains the reason for having done so.
A client SHOULD NOT unilaterally close the connection, and instead
SHOULD issue a LOGOUT command. If the server detects that the client
has unilaterally closed the connection, the server MAY omit the
untagged BYE response and simply close its connection.
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+----------------------+
|connection established|
+----------------------+
||
\/
+--------------------------------------+
| server greeting |
+--------------------------------------+
|| (1) || (2) || (3)
\/ || ||
+-----------------+ || ||
|Not Authenticated| || ||
+-----------------+ || ||
|| (7) || (4) || ||
|| \/ \/ ||
|| +----------------+ ||
|| | Authenticated |<=++ ||
|| +----------------+ || ||
|| || (7) || (5) || (6) ||
|| || \/ || ||
|| || +--------+ || ||
|| || |Selected|==++ ||
|| || +--------+ ||
|| || || (7) ||
\/ \/ \/ \/
+--------------------------------------+
| Logout |
+--------------------------------------+
||
\/
+-------------------------------+
|both sides close the connection|
+-------------------------------+
(1) connection without pre-authentication (OK greeting)
(2) pre-authenticated connection (PREAUTH greeting)
(3) rejected connection (BYE greeting)
(4) successful LOGIN or AUTHENTICATE command
(5) successful SELECT or EXAMINE command
(6) CLOSE command, or failed SELECT or EXAMINE command
(7) LOGOUT command, server shutdown, or connection closed
4. Data Formats
IMAP4rev1 uses textual commands and responses. Data in IMAP4rev1 can
be in one of several forms: atom, number, string, parenthesized list,
or NIL. Note that a particular data item may take more than one
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form; for example, a data item defined as using "astring" syntax may
be either an atom or a string.
4.1. Atom
An atom consists of one or more non-special characters.
4.2. Number
A number consists of one or more digit characters, and represents a
numeric value.
4.3. String
A string is in one of two forms: either literal or quoted string.
The literal form is the general form of string. The quoted string
form is an alternative that avoids the overhead of processing a
literal at the cost of limitations of characters which may be used.
A literal is a sequence of zero or more octets (including CR and LF),
prefix-quoted with an octet count in the form of an open brace ("{"),
the number of octets, close brace ("}"), and CRLF. In the case of
literals transmitted from server to client, the CRLF is immediately
followed by the octet data. In the case of literals transmitted from
client to server, the client MUST wait to receive a command
continuation request (described later in this document) before
sending the octet data (and the remainder of the command).
A quoted string is a sequence of zero or more 7-bit characters,
excluding CR and LF, with double quote (<">) characters at each end.
The empty string is represented as either "" (a quoted string with
zero characters between double quotes) or as {0} followed by CRLF (a
literal with an octet count of 0).
Note: Even if the octet count is 0, a client transmitting a
literal MUST wait to receive a command continuation request.
4.3.1. 8-bit and Binary Strings
8-bit textual and binary mail is supported through the use of a
[MIME-IMB] content transfer encoding. IMAP4rev1 implementations MAY
transmit 8-bit or multi-octet characters in literals, but SHOULD do
so only when the [CHARSET] is identified.
Although a BINARY body encoding is defined, unencoded binary strings
are not permitted. A "binary string" is any string with NUL
characters. Implementations MUST encode binary data into a textual
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form, such as BASE64, before transmitting the data. A string with an
excessive amount of CTL characters MAY also be considered to be
binary.
4.4. Parenthesized List
Data structures are represented as a "parenthesized list"; a sequence
of data items, delimited by space, and bounded at each end by
parentheses. A parenthesized list can contain other parenthesized
lists, using multiple levels of parentheses to indicate nesting.
The empty list is represented as () -- a parenthesized list with no
members.
4.5. NIL
The special form "NIL" represents the non-existence of a particular
data item that is represented as a string or parenthesized list, as
distinct from the empty string "" or the empty parenthesized list ().
Note: NIL is never used for any data item which takes the form of
an atom. For example, a mailbox name of "NIL" is a mailbox named
NIL as opposed to a non-existent mailbox name. This is because
mailbox uses "astring" syntax which is an atom or a string.
Conversely, an addr-name of NIL is a non-existent personal name,
because addr-name uses "nstring" syntax which is NIL or a string,
but never an atom.
5. Operational Considerations
The following rules are listed here to ensure that all IMAP4rev1
implementations interoperate properly.
5.1. Mailbox Naming
Mailbox names are 7-bit. Client implementations MUST NOT attempt to
create 8-bit mailbox names, and SHOULD interpret any 8-bit mailbox
names returned by LIST or LSUB as UTF-8. Server implementations
SHOULD prohibit the creation of 8-bit mailbox names, and SHOULD NOT
return 8-bit mailbox names in LIST or LSUB. See Section 5.1.3 for
more information on how to represent non-ASCII mailbox names.
Note: 8-bit mailbox names were undefined in earlier versions of
this protocol. Some sites used a local 8-bit character set to
represent non-ASCII mailbox names. Such usage is not
interoperable, and is now formally deprecated.
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The case-insensitive mailbox name INBOX is a special name reserved to
mean "the primary mailbox for this user on this server". (Note that
this special name may not exist on some servers for some users.) The
interpretation of all other names is implementation-dependent.
In particular, this specification takes no position on case
sensitivity in non-INBOX mailbox names. Some server implementations
are fully case-sensitive; others preserve case of a newly-created
name but otherwise are case-insensitive; and yet others coerce names
to a particular case. Client implementations MUST interact with any
of these. If a server implementation interprets non-INBOX mailbox
names as case-insensitive, it MUST treat names using the
international naming convention specially as described in
Section 5.1.3.
There are certain client considerations when creating a new mailbox
name:
1. Any character which is one of the atom-specials (see the Formal
Syntax) will require that the mailbox name be represented as a
quoted string or literal.
2. CTL and other non-graphic characters are difficult to represent
in a user interface and are best avoided.
3. Although the list-wildcard characters ("%" and "*") are valid in
a mailbox name, it is difficult to use such mailbox names with
the LIST and LSUB commands due to the conflict with wildcard
interpretation.
4. Usually, a character (determined by the server implementation) is
reserved to delimit levels of hierarchy.
5. Two characters, "#" and "&", have meanings by convention, and
should be avoided except when used in that convention.
5.1.1. Mailbox Hierarchy Naming
If it is desired to export hierarchical mailbox names, mailbox names
MUST be left-to-right hierarchical using a single character to
separate levels of hierarchy. The same hierarchy separator character
is used for all levels of hierarchy within a single name.
5.1.2. Mailbox Namespace Naming Convention
By convention, the first hierarchical element of any mailbox name
which begins with "#" identifies the "namespace" of the remainder of
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the name. This makes it possible to disambiguate between different
types of mailbox stores, each of which have their own namespaces.
For example, implementations which offer access to USENET
newsgroups MAY use the "#news" namespace to partition the USENET
newsgroup namespace from that of other mailboxes. Thus, the
comp.mail.misc newsgroup would have a mailbox name of
"#news.comp.mail.misc", and the name "comp.mail.misc" can refer to
a different object (e.g., a user's private mailbox).
5.1.3. Mailbox International Naming Convention
By convention, international mailbox names in IMAP4rev1 are specified
using a modified version of the UTF-7 encoding described in [UTF-7].
Modified UTF-7 may also be usable in servers that implement an
earlier version of this protocol.
In modified UTF-7, printable US-ASCII characters, except for "&",
represent themselves; that is, characters with octet values 0x20-0x25
and 0x27-0x7e. The character "&" (0x26) is represented by the two-
octet sequence "&-".
All other characters (octet values 0x00-0x1f and 0x7f-0xff) are
represented in modified BASE64, with a further modification from
[UTF-7] that "," is used instead of "/". Modified BASE64 MUST NOT be
used to represent any printing US-ASCII character which can represent
itself. Only characters inside the modified BASE64 alphabet are
permitted in modified BASE64 text.
"&" is used to shift to modified BASE64 and "-" to shift back to US-
ASCII. There is no implicit shift from BASE64 to US-ASCII, and null
shifts ("-&" while in BASE64; note that "&-" while in US-ASCII means
"&") are not permitted. However, all names start in US-ASCII, and
MUST end in US-ASCII; that is, a name that ends with a non-ASCII
ISO-10646 character MUST end with a "-").
The purpose of these modifications is to correct the following
problems with UTF-7:
1. UTF-7 uses the "+" character for shifting; this conflicts with
the common use of "+" in mailbox names, in particular USENET
newsgroup names.
2. UTF-7's encoding is BASE64 which uses the "/" character; this
conflicts with the use of "/" as a popular hierarchy delimiter.
3. UTF-7 prohibits the unencoded usage of "\"; this conflicts with
the use of "\" as a popular hierarchy delimiter.
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4. UTF-7 prohibits the unencoded usage of "~"; this conflicts with
the use of "~" in some servers as a home directory indicator.
5. UTF-7 permits multiple alternate forms to represent the same
string; in particular, printable US-ASCII characters can be
represented in encoded form.
Although modified UTF-7 is a convention, it establishes certain
requirements on server handling of any mailbox name with an embedded
"&" character. In particular, server implementations MUST preserve
the exact form of the modified BASE64 portion of a modified UTF-7
name and treat that text as case-sensitive, even if names are
otherwise case-insensitive or case-folded.
Server implementations SHOULD verify that any mailbox name with an
embedded "&" character, used as an argument to CREATE, is: in the
correctly modified UTF-7 syntax, has no superfluous shifts, and has
no encoding in modified BASE64 of any printing US-ASCII character
which can represent itself. However, client implementations MUST NOT
depend upon the server doing this, and SHOULD NOT attempt to create a
mailbox name with an embedded "&" character unless it complies with
the modified UTF-7 syntax.
Server implementations which export a mail store that does not follow
the modified UTF-7 convention MUST convert to modified UTF-7 any
mailbox name that contains either non-ASCII characters or the "&"
character.
For example, here is a mailbox name which mixes English, Chinese,
and Japanese text: ~peter/mail/&U,BTFw-/&ZeVnLIqe-
For example, the string "&Jjo!" is not a valid mailbox name
because it does not contain a shift to US-ASCII before the "!".
The correct form is "&Jjo-!". The string "&U,BTFw-&ZeVnLIqe-" is
not permitted because it contains a superfluous shift. The
correct form is "&U,BTF2XlZyyKng-".
5.2. Mailbox Size and Message Status Updates
At any time, a server can send data that the client did not request.
Sometimes, such behavior is REQUIRED. For example, agents other than
the server MAY add messages to the mailbox (e.g., new message
delivery), change the flags of the messages in the mailbox (e.g.,
simultaneous access to the same mailbox by multiple agents), or even
remove messages from the mailbox. A server MUST send mailbox size
updates automatically if a mailbox size change is observed during the
processing of a command. A server SHOULD send message flag updates
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automatically, without requiring the client to request such updates
explicitly.
Special rules exist for server notification of a client about the
removal of messages to prevent synchronization errors; see the
description of the EXPUNGE response for more detail. In particular,
it is NOT permitted to send an EXISTS response that would reduce the
number of messages in the mailbox; only the EXPUNGE response can do
this.
Regardless of what implementation decisions a client makes on
remembering data from the server, a client implementation MUST record
mailbox size updates. It MUST NOT assume that any command after the
initial mailbox selection will return the size of the mailbox.
5.3. Response when no Command in Progress
Server implementations are permitted to send an untagged response
(except for EXPUNGE) while there is no command in progress. Server
implementations that send such responses MUST deal with flow control
considerations. Specifically, they MUST either (1) verify that the
size of the data does not exceed the underlying transport's available
window size, or (2) use non-blocking writes.
5.4. Autologout Timer
If a server has an inactivity autologout timer that applies to
sessions after authentication, the duration of that timer MUST be at
least 30 minutes. The receipt of ANY command from the client during
that interval SHOULD suffice to reset the autologout timer.
5.5. Multiple Commands in Progress
The client MAY send another command without waiting for the
completion result response of a command, subject to ambiguity rules
(see below) and flow control constraints on the underlying data
stream. Similarly, a server MAY begin processing another command
before processing the current command to completion, subject to
ambiguity rules. However, any command continuation request responses
and command continuations MUST be negotiated before any subsequent
command is initiated.
The exception is if an ambiguity would result because of a command
that would affect the results of other commands. Clients MUST NOT
send multiple commands without waiting if an ambiguity would result.
If the server detects a possible ambiguity, it MUST execute commands
to completion in the order given by the client.
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The most obvious example of ambiguity is when a command would affect
the results of another command, e.g., a FETCH of a message's flags
and a STORE of that same message's flags.
A non-obvious ambiguity occurs with commands that permit an untagged
EXPUNGE response (commands other than FETCH, STORE, and SEARCH),
since an untagged EXPUNGE response can invalidate sequence numbers in
a subsequent command. This is not a problem for FETCH, STORE, or
SEARCH commands because servers are prohibited from sending EXPUNGE
responses while any of those commands are in progress. Therefore, if
the client sends any command other than FETCH, STORE, or SEARCH, it
MUST wait for the completion result response before sending a command
with message sequence numbers.
Note: EXPUNGE responses are permitted while UID FETCH, UID STORE,
and UID SEARCH are in progress. If the client sends a UID
command, it MUST wait for a completion result response before
sending a command which uses message sequence numbers (this may
include UID SEARCH). Any message sequence numbers in an argument
to UID SEARCH are associated with messages prior to the effect of
any untagged EXPUNGE returned by the UID SEARCH.
For example, the following non-waiting command sequences are invalid:
FETCH + NOOP + STORE
STORE + COPY + FETCH
COPY + COPY
CHECK + FETCH
The following are examples of valid non-waiting command sequences:
FETCH + STORE + SEARCH + CHECK
STORE + COPY + EXPUNGE
UID SEARCH + UID SEARCH may be valid or invalid as a non-waiting
command sequence, depending upon whether or not the second UID
SEARCH contains message sequence numbers.
6. Client Commands
IMAP4rev1 commands are described in this section. Commands are
organized by the state in which the command is permitted. Commands
which are permitted in multiple states are listed in the minimum
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permitted state (for example, commands valid in authenticated and
selected state are listed in the authenticated state commands).
Command arguments, identified by "Arguments:" in the command
descriptions below, are described by function, not by syntax. The
precise syntax of command arguments is described in the Formal Syntax
(Section 9).
Some commands cause specific server responses to be returned; these
are identified by "Responses:" in the command descriptions below.
See the response descriptions in the Responses section for
information on these responses, and the Formal Syntax section for the
precise syntax of these responses. It is possible for server data to
be transmitted as a result of any command. Thus, commands that do
not specifically require server data specify "no specific responses
for this command" instead of "none".
The "Result:" in the command description refers to the possible
tagged status responses to a command, and any special interpretation
of these status responses.
The state of a connection is only changed by successful commands
which are documented as changing state. A rejected command (BAD
response) never changes the state of the connection or of the
selected mailbox. A failed command (NO response) generally does not
change the state of the connection or of the selected mailbox; the
exception being the SELECT and EXAMINE commands.
6.1. Client Commands - Any State
The following commands are valid in any state: CAPABILITY, NOOP, and
LOGOUT.
6.1.1. CAPABILITY Command
Arguments: none
Responses: REQUIRED untagged response: CAPABILITY
Result: OK - capability completed
BAD - command unknown or arguments invalid
The CAPABILITY command requests a listing of capabilities that the
server supports. The server MUST send a single untagged CAPABILITY
response with "IMAP4rev1" as one of the listed capabilities before
the (tagged) OK response.
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A capability name which begins with "AUTH=" indicates that the server
supports that particular authentication mechanism. All such names
are, by definition, part of this specification. For example, the
authorization capability for an experimental "blurdybloop"
authenticator would be "AUTH=XBLURDYBLOOP" and not
"XAUTH=BLURDYBLOOP" or "XAUTH=XBLURDYBLOOP".
Other capability names refer to extensions, revisions, or amendments
to this specification. See the documentation of the CAPABILITY
response for additional information. No capabilities, beyond the
base IMAP4rev1 set defined in this specification, are enabled without
explicit client action to invoke the capability.
Client and server implementations MUST implement the STARTTLS,
LOGINDISABLED, and AUTH=PLAIN (described in [PLAIN]) capabilities.
See the Security Considerations section for important information.
See the section entitled "Client Commands - Experimental/Expansion"
for information about the form of site or implementation-specific
capabilities.
Example: C: abcd CAPABILITY
S: * CAPABILITY IMAP4rev1 STARTTLS AUTH=GSSAPI
LOGINDISABLED
S: abcd OK CAPABILITY completed
C: efgh STARTTLS
S: efgh OK STARTLS completed
<TLS negotiation, further commands are under [TLS] layer>
C: ijkl CAPABILITY
S: * CAPABILITY IMAP4rev1 AUTH=GSSAPI AUTH=PLAIN
S: ijkl OK CAPABILITY completed
6.1.2. NOOP Command
Arguments: none
Responses: no specific responses for this command (but see below)
Result: OK - noop completed
BAD - command unknown or arguments invalid
The NOOP command always succeeds. It does nothing.
Since any command can return a status update as untagged data, the
NOOP command can be used as a periodic poll for new messages or
message status updates during a period of inactivity (this is the
preferred method to do this). The NOOP command can also be used to
reset any inactivity autologout timer on the server.
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Example: C: a002 NOOP
S: a002 OK NOOP completed
. . .
C: a047 NOOP
S: * 22 EXPUNGE
S: * 23 EXISTS
S: * 3 RECENT
S: * 14 FETCH (FLAGS (\Seen \Deleted))
S: a047 OK NOOP completed
6.1.3. LOGOUT Command
Arguments: none
Responses: REQUIRED untagged response: BYE
Result: OK - logout completed
BAD - command unknown or arguments invalid
The LOGOUT command informs the server that the client is done with
the connection. The server MUST send a BYE untagged response before
the (tagged) OK response, and then close the network connection.
Example: C: A023 LOGOUT
S: * BYE IMAP4rev1 Server logging out
S: A023 OK LOGOUT completed
(Server and client then close the connection)
6.2. Client Commands - Not Authenticated State
In the not authenticated state, the AUTHENTICATE or LOGIN command
establishes authentication and enters the authenticated state. The
AUTHENTICATE command provides a general mechanism for a variety of
authentication techniques, privacy protection, and integrity
checking; whereas the LOGIN command uses a traditional user name and
plaintext password pair and has no means of establishing privacy
protection or integrity checking.
The STARTTLS command is an alternate form of establishing session
privacy protection and integrity checking, but does not establish
authentication or enter the authenticated state.
Server implementations MAY allow access to certain mailboxes without
establishing authentication. This can be done by means of the
ANONYMOUS [SASL] authenticator described in [ANONYMOUS]. An older
convention is a LOGIN command using the userid "anonymous"; in this
case, a password is required although the server may choose to accept
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any password. The restrictions placed on anonymous users are
implementation-dependent.
Once authenticated (including as anonymous), it is not possible to
re-enter not authenticated state.
In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT),
the following commands are valid in the not authenticated state:
STARTTLS, AUTHENTICATE and LOGIN. See the Security Considerations
section for important information about these commands.
6.2.1. STARTTLS Command
Arguments: none
Responses: no specific response for this command
Result: OK - starttls completed, begin TLS negotiation
BAD - command unknown or arguments invalid
A [TLS] negotiation begins immediately after the CRLF at the end of
the tagged OK response from the server. Once a client issues a
STARTTLS command, it MUST NOT issue further commands until a server
response is seen and the [TLS] negotiation is complete.
The server remains in the non-authenticated state, even if client
credentials are supplied during the [TLS] negotiation. This does not
preclude an authentication mechanism such as EXTERNAL (defined in
[SASL]) from using client identity determined by the [TLS]
negotiation.
Once [TLS] has been started, the client MUST discard cached
information about server capabilities and SHOULD re-issue the
CAPABILITY command. This is necessary to protect against man-in-
the-middle attacks which alter the capabilities list prior to
STARTTLS. The server MAY advertise different capabilities, and in
particular SHOULD NOT advertise the STARTTLS capability, after a
successful STARTTLS command.
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Example: C: a001 CAPABILITY
S: * CAPABILITY IMAP4rev1 STARTTLS LOGINDISABLED
S: a001 OK CAPABILITY completed
C: a002 STARTTLS
S: a002 OK Begin TLS negotiation now
<TLS negotiation, further commands are under [TLS] layer>
C: a003 CAPABILITY
S: * CAPABILITY IMAP4rev1 AUTH=PLAIN
S: a003 OK CAPABILITY completed
C: a004 LOGIN joe password
S: a004 OK LOGIN completed
6.2.2. AUTHENTICATE Command
Arguments: authentication mechanism name
Responses: continuation data can be requested
Result: OK - authenticate completed, now in authenticated state
NO - authenticate failure: unsupported authentication
mechanism, credentials rejected
BAD - command unknown or arguments invalid,
authentication exchange cancelled
The AUTHENTICATE command indicates a [SASL] authentication mechanism
to the server. If the server supports the requested authentication
mechanism, it performs an authentication protocol exchange to
authenticate and identify the client. It MAY also negotiate an
OPTIONAL security layer for subsequent protocol interactions. If the
requested authentication mechanism is not supported, the server
SHOULD reject the AUTHENTICATE command by sending a tagged NO
response.
The AUTHENTICATE command does not support the optional "initial
response" feature of [SASL]. Section 3 of [SASL] specifies how to
handle an authentication mechanism which uses an initial response.
The service name specified by this protocol's profile of [SASL] is
"imap".
The authentication protocol exchange consists of a series of server
challenges and client responses that are specific to the
authentication mechanism. A server challenge consists of a command
continuation request response with the "+" token followed by a BASE64
encoded string. The client response consists of a single line
consisting of a BASE64 encoded string. If the client wishes to
cancel an authentication exchange, it issues a line consisting of a
single "*". If the server receives such a response, or if it
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receives an invalid BASE64 string (e.g. characters outside the
BASE64 alphabet, or non-terminal "="), it MUST reject the
AUTHENTICATE command by sending a tagged BAD response.
If a security layer is negotiated through the [SASL] authentication
exchange, it takes effect immediately following the CRLF that
concludes the authentication exchange for the client, and the CRLF of
the tagged OK response for the server.
While client and server implementations MUST implement the
AUTHENTICATE command itself, it is not required to implement any
authentication mechanisms other than the PLAIN mechanism described in
[PLAIN]. Also, an authentication mechanism is not required to
support any security layers.
Note: a server implementation MUST implement a configuration in
which it does NOT permit any plaintext password mechanisms, unless
either the STARTTLS command has been negotiated or some other
mechanism that protects the session from password snooping has
been provided. Server sites SHOULD NOT use any configuration
which permits a plaintext password mechanism without such a
protection mechanism against password snooping. Client and server
implementations SHOULD implement additional [SASL] mechanisms that
do not use plaintext passwords, such the GSSAPI mechanism
described in [SASL] and/or the [DIGEST-MD5] mechanism.
Servers and clients can support multiple authentication mechanisms.
The server SHOULD list its supported authentication mechanisms in the
response to the CAPABILITY command so that the client knows which
authentication mechanisms to use.
A server MAY include a CAPABILITY response code in the tagged OK
response of a successful AUTHENTICATE command in order to send
capabilities automatically. It is unnecessary for a client to send a
separate CAPABILITY command if it recognizes these automatic
capabilities. This should only be done if a security layer was not
negotiated by the AUTHENTICATE command, because the tagged OK
response as part of an AUTHENTICATE command is not protected by
encryption/integrity checking. [SASL] requires the client to re-
issue a CAPABILITY command in this case. The server MAY advertise
different capabilities after a successful AUTHENTICATE command.
If an AUTHENTICATE command fails with a NO response, the client MAY
try another authentication mechanism by issuing another AUTHENTICATE
command. It MAY also attempt to authenticate by using the LOGIN
command (see Section 6.2.3 for more detail). In other words, the
client MAY request authentication types in decreasing order of
preference, with the LOGIN command as a last resort.
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The authorization identity passed from the client to the server
during the authentication exchange is interpreted by the server as
the user name whose privileges the client is requesting.
Example: S: * OK IMAP4rev1 Server
C: A001 AUTHENTICATE GSSAPI
S: +
C: YIIB+wYJKoZIhvcSAQICAQBuggHqMIIB5qADAgEFoQMCAQ6iBw
MFACAAAACjggEmYYIBIjCCAR6gAwIBBaESGxB1Lndhc2hpbmd0
b24uZWR1oi0wK6ADAgEDoSQwIhsEaW1hcBsac2hpdmFtcy5jYW
Mud2FzaGluZ3Rvbi5lZHWjgdMwgdCgAwIBAaEDAgEDooHDBIHA
cS1GSa5b+fXnPZNmXB9SjL8Ollj2SKyb+3S0iXMljen/jNkpJX
AleKTz6BQPzj8duz8EtoOuNfKgweViyn/9B9bccy1uuAE2HI0y
C/PHXNNU9ZrBziJ8Lm0tTNc98kUpjXnHZhsMcz5Mx2GR6dGknb
I0iaGcRerMUsWOuBmKKKRmVMMdR9T3EZdpqsBd7jZCNMWotjhi
vd5zovQlFqQ2Wjc2+y46vKP/iXxWIuQJuDiisyXF0Y8+5GTpAL
pHDc1/pIGmMIGjoAMCAQGigZsEgZg2on5mSuxoDHEA1w9bcW9n
FdFxDKpdrQhVGVRDIzcCMCTzvUboqb5KjY1NJKJsfjRQiBYBdE
NKfzK+g5DlV8nrw81uOcP8NOQCLR5XkoMHC0Dr/80ziQzbNqhx
O6652Npft0LQwJvenwDI13YxpwOdMXzkWZN/XrEqOWp6GCgXTB
vCyLWLlWnbaUkZdEYbKHBPjd8t/1x5Yg==
S: + YGgGCSqGSIb3EgECAgIAb1kwV6ADAgEFoQMCAQ+iSzBJoAMC
AQGiQgRAtHTEuOP2BXb9sBYFR4SJlDZxmg39IxmRBOhXRKdDA0
uHTCOT9Bq3OsUTXUlk0CsFLoa8j+gvGDlgHuqzWHPSQg==
C:
S: + YDMGCSqGSIb3EgECAgIBAAD/////6jcyG4GE3KkTzBeBiVHe
ceP2CWY0SR0fAQAgAAQEBAQ=
C: YDMGCSqGSIb3EgECAgIBAAD/////3LQBHXTpFfZgrejpLlLImP
wkhbfa2QteAQAgAG1yYwE=
S: A001 OK GSSAPI authentication successful
Note: The line breaks within server challenges and client responses
are for editorial clarity and are not in real authenticators.
6.2.3. LOGIN Command
Arguments: user name
password
Responses: no specific responses for this command
Result: OK - login completed, now in authenticated state
NO - login failure: user name or password rejected
BAD - command unknown or arguments invalid
The LOGIN command identifies the client to the server and carries the
plaintext password authenticating this user.
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A server MAY include a CAPABILITY response code in the tagged OK
response to a successful LOGIN command in order to send capabilities
automatically. It is unnecessary for a client to send a separate
CAPABILITY command if it recognizes these automatic capabilities.
Example: C: a001 LOGIN SMITH SESAME
S: a001 OK LOGIN completed
Note: Use of the LOGIN command over an insecure network (such as the
Internet) is a security risk, because anyone monitoring network
traffic can obtain plaintext passwords. The LOGIN command SHOULD NOT
be used except as a last resort, and it is recommended that client
implementations have a means to disable any automatic use of the
LOGIN command.
Unless either the STARTTLS command has been negotiated or some other
mechanism that protects the session from password snooping has been
provided, a server implementation MUST implement a configuration in
which it advertises the LOGINDISABLED capability and does NOT permit
the LOGIN command. Server sites SHOULD NOT use any configuration
which permits the LOGIN command without such a protection mechanism
against password snooping. A client implementation MUST NOT send a
LOGIN command if the LOGINDISABLED capability is advertised.
6.3. Client Commands - Authenticated State
In the authenticated state, commands that manipulate mailboxes as
atomic entities are permitted. Of these commands, the SELECT and
EXAMINE commands will select a mailbox for access and enter the
selected state.
In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT),
the following commands are valid in the authenticated state: SELECT,
EXAMINE, CREATE, DELETE, RENAME, SUBSCRIBE, UNSUBSCRIBE, LIST, LSUB,
STATUS, and APPEND.
6.3.1. SELECT Command
Arguments: mailbox name
Responses: REQUIRED untagged responses: FLAGS, EXISTS, RECENT
REQUIRED OK untagged responses: UNSEEN (if any unseen
exist), PERMANENTFLAGS,
UIDNEXT, UIDVALIDITY
Result: OK - select completed, now in selected state
NO - select failure, now in authenticated state: no
such mailbox, can't access mailbox
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BAD - command unknown or arguments invalid
The SELECT command selects a mailbox so that messages in the mailbox
can be accessed. Before returning an OK to the client, the server
MUST send the following untagged data to the client. Note that
earlier versions of this protocol only required the FLAGS, EXISTS,
and RECENT untagged data; consequently, client implementations SHOULD
implement default behavior for missing data as discussed with the
individual item.
FLAGS Defined flags in the mailbox. See the description of the
FLAGS response for more detail.
<n> EXISTS The number of messages in the mailbox. See the
description of the EXISTS response for more detail.
<n> RECENT The number of messages with the \Recent flag set. See
the description of the RECENT response for more detail.
OK [UNSEEN <n>] The message sequence number of the first unseen
message in the mailbox. If there are any unseen messages in the
mailbox, an UNSEEN response MUST be sent, if not it MUST be
omitted. If this is missing, the client can not make any
assumptions about the first unseen message in the mailbox, and
needs to issue a SEARCH command if it wants to find it.
OK [PERMANENTFLAGS (<list of flags>)] A list of message flags that
the client can change permanently. If this is missing, the client
should assume that all flags can be changed permanently.
OK [UIDNEXT <n>] The next unique identifier value. Refer to
Section 2.3.1.1 for more information. If this is missing, the
client can not make any assumptions about the next unique
identifier value.
OK [UIDVALIDITY <n>] The unique identifier validity value. Refer to
Section 2.3.1.1 for more information. If this is missing, the
server does not support unique identifiers.
Only one mailbox can be selected at a time in a connection;
simultaneous access to multiple mailboxes requires multiple
connections. The SELECT command automatically deselects any
currently selected mailbox before attempting the new selection.
Consequently, if a mailbox is selected and a SELECT command that
fails is attempted, no mailbox is selected.
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If the client is permitted to modify the mailbox, the server SHOULD
prefix the text of the tagged OK response with the "[READ-WRITE]"
response code.
If the client is not permitted to modify the mailbox but is permitted
read access, the mailbox is selected as read-only, and the server
MUST prefix the text of the tagged OK response to SELECT with the
"[READ-ONLY]" response code. Read-only access through SELECT differs
from the EXAMINE command in that certain read-only mailboxes MAY
permit the change of permanent state on a per-user (as opposed to
global) basis. Netnews messages marked in a server-based .newsrc
file are an example of such per-user permanent state that can be
modified with read-only mailboxes.
Example: C: A142 SELECT INBOX
S: * 172 EXISTS
S: * 1 RECENT
S: * OK [UNSEEN 12] Message 12 is first unseen
S: * OK [UIDVALIDITY 3857529045] UIDs valid
S: * OK [UIDNEXT 4392] Predicted next UID
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited
S: A142 OK [READ-WRITE] SELECT completed
6.3.2. EXAMINE Command
Arguments: mailbox name
Responses: REQUIRED untagged responses: FLAGS, EXISTS, RECENT
REQUIRED OK untagged responses: UNSEEN, PERMANENTFLAGS,
UIDNEXT, UIDVALIDITY
Result: OK - examine completed, now in selected state
NO - examine failure, now in authenticated state: no
such mailbox, can't access mailbox BAD - command unknown
or arguments invalid
The EXAMINE command is identical to SELECT and returns the same
output; however, the selected mailbox is identified as read-only. No
changes to the permanent state of the mailbox, including per-user
state, are permitted; in particular, EXAMINE MUST NOT cause messages
to lose the \Recent flag.
The text of the tagged OK response to the EXAMINE command MUST begin
with the "[READ-ONLY]" response code.
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Example: C: A932 EXAMINE blurdybloop
S: * 17 EXISTS
S: * 2 RECENT
S: * OK [UNSEEN 8] Message 8 is first unseen
S: * OK [UIDVALIDITY 3857529045] UIDs valid
S: * OK [UIDNEXT 4392] Predicted next UID
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
S: * OK [PERMANENTFLAGS ()] No permanent flags permitted
S: A932 OK [READ-ONLY] EXAMINE completed
6.3.3. CREATE Command
Arguments: mailbox name
Responses: no specific responses for this command
Result: OK - create completed
NO - create failure: can't create mailbox with that name
BAD - command unknown or arguments invalid
The CREATE command creates a mailbox with the given name. An OK
response is returned only if a new mailbox with that name has been
created. It is an error to attempt to create INBOX or a mailbox with
a name that refers to an extant mailbox. Any error in creation will
return a tagged NO response.
If the mailbox name is suffixed with the server's hierarchy separator
character (as returned from the server by a LIST command), this is a
declaration that the client intends to create mailbox names under
this name in the hierarchy. Server implementations that do not
require this declaration MUST ignore the declaration. In any case,
the name created is without the trailing hierarchy delimiter.
If the server's hierarchy separator character appears elsewhere in
the name, the server SHOULD create any superior hierarchical names
that are needed for the CREATE command to be successfully completed.
In other words, an attempt to create "foo/bar/zap" on a server in
which "/" is the hierarchy separator character SHOULD create foo/ and
foo/bar/ if they do not already exist.
If a new mailbox is created with the same name as a mailbox which was
deleted, its unique identifiers MUST be greater than any unique
identifiers used in the previous incarnation of the mailbox UNLESS
the new incarnation has a different unique identifier validity value.
See the description of the UID command for more detail.
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Example: C: A003 CREATE owatagusiam/
S: A003 OK CREATE completed
C: A004 CREATE owatagusiam/blurdybloop
S: A004 OK CREATE completed
Note: The interpretation of this example depends on whether "/"
was returned as the hierarchy separator from LIST. If "/" is the
hierarchy separator, a new level of hierarchy named "owatagusiam"
with a member called "blurdybloop" is created. Otherwise, two
mailboxes at the same hierarchy level are created.
6.3.4. DELETE Command
Arguments: mailbox name
Responses: no specific responses for this command
Result: OK - delete completed
NO - delete failure: can't delete mailbox with that name
BAD - command unknown or arguments invalid
The DELETE command permanently removes the mailbox with the given
name. A tagged OK response is returned only if the mailbox has been
deleted. It is an error to attempt to delete INBOX or a mailbox name
that does not exist.
The DELETE command MUST NOT remove inferior hierarchical names. For
example, if a mailbox "foo" has an inferior "foo.bar" (assuming "."
is the hierarchy delimiter character), removing "foo" MUST NOT remove
"foo.bar". It is an error to attempt to delete a name that has
inferior hierarchical names and also has the \Noselect mailbox name
attribute (see the description of the LIST response for more
details).
It is permitted to delete a name that has inferior hierarchical names
and does not have the \Noselect mailbox name attribute. If the
server implementation does not permit deleting the name while
inferior hierarchical names exists the \Noselect mailbox name
attribute is set for that name. In any case, all messages in that
mailbox are removed by the DELETE command.
The value of the highest-used unique identifier of the deleted
mailbox MUST be preserved so that a new mailbox created with the same
name will not reuse the identifiers of the former incarnation, UNLESS
the new incarnation has a different unique identifier validity value.
See the description of the UID command for more detail.
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Examples: C: A682 LIST "" *
S: * LIST () "/" blurdybloop
S: * LIST (\Noselect) "/" foo
S: * LIST () "/" foo/bar
S: A682 OK LIST completed
C: A683 DELETE blurdybloop
S: A683 OK DELETE completed
C: A684 DELETE foo
S: A684 NO Name "foo" has inferior hierarchical names
C: A685 DELETE foo/bar
S: A685 OK DELETE Completed
C: A686 LIST "" *
S: * LIST (\Noselect) "/" foo
S: A686 OK LIST completed
C: A687 DELETE foo
S: A687 OK DELETE Completed
C: A82 LIST "" *
S: * LIST () "." blurdybloop
S: * LIST () "." foo
S: * LIST () "." foo.bar
S: A82 OK LIST completed
C: A83 DELETE blurdybloop
S: A83 OK DELETE completed
C: A84 DELETE foo
S: A84 OK DELETE Completed
C: A85 LIST "" *
S: * LIST () "." foo.bar
S: A85 OK LIST completed
C: A86 LIST "" %
S: * LIST (\Noselect) "." foo
S: A86 OK LIST completed
6.3.5. RENAME Command
Arguments: existing mailbox name
new mailbox name
Responses: no specific responses for this command
Result: OK - rename completed
NO - rename failure: can't rename mailbox with that name,
can't rename to mailbox with that name
BAD - command unknown or arguments invalid
The RENAME command changes the name of a mailbox. A tagged OK
response is returned only if the mailbox has been renamed. It is an
error to attempt to rename from a mailbox name that does not exist or
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to a mailbox name that already exists. Any error in renaming will
return a tagged NO response.
If the name has inferior hierarchical names, then the inferior
hierarchical names MUST also be renamed. For example, a rename of
"foo" to "zap" will rename "foo/bar" (assuming "/" is the hierarchy
delimiter character) to "zap/bar".
If the server's hierarchy separator character appears in the name,
the server SHOULD create any superior hierarchical names that are
needed for the RENAME command to complete successfully. In other
words, an attempt to rename "foo/bar/zap" to baz/rag/zowie on a
server in which "/" is the hierarchy separator character SHOULD
create baz/ and baz/rag/ if they do not already exist.
The value of the highest-used unique identifier of the old mailbox
name MUST be preserved so that a new mailbox created with the same
name will not reuse the identifiers of the former incarnation, UNLESS
the new incarnation has a different unique identifier validity value.
See the description of the UID command for more detail.
Renaming INBOX is permitted, and has special behavior. It moves all
messages in INBOX to a new mailbox with the given name, leaving INBOX
empty. If the server implementation supports inferior hierarchical
names of INBOX, these are unaffected by a rename of INBOX.
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Examples: C: A682 LIST "" *
S: * LIST () "/" blurdybloop
S: * LIST (\Noselect) "/" foo
S: * LIST () "/" foo/bar
S: A682 OK LIST completed
C: A683 RENAME blurdybloop sarasoop
S: A683 OK RENAME completed
C: A684 RENAME foo zowie
S: A684 OK RENAME Completed
C: A685 LIST "" *
S: * LIST () "/" sarasoop
S: * LIST (\Noselect) "/" zowie
S: * LIST () "/" zowie/bar
S: A685 OK LIST completed
C: Z432 LIST "" *
S: * LIST () "." INBOX
S: * LIST () "." INBOX.bar
S: Z432 OK LIST completed
C: Z433 RENAME INBOX old-mail
S: Z433 OK RENAME completed
C: Z434 LIST "" *
S: * LIST () "." INBOX
S: * LIST () "." INBOX.bar
S: * LIST () "." old-mail
S: Z434 OK LIST completed
6.3.6. SUBSCRIBE Command
Arguments: mailbox
Responses: no specific responses for this command
Result: OK - subscribe completed
NO - subscribe failure: can't subscribe to that name
BAD - command unknown or arguments invalid
The SUBSCRIBE command adds the specified mailbox name to the server's
set of "active" or "subscribed" mailboxes as returned by the LSUB
command. This command returns a tagged OK response only if the
subscription is successful.
A server MAY validate the mailbox argument to SUBSCRIBE to verify
that it exists. However, it MUST NOT unilaterally remove an existing
mailbox name from the subscription list even if a mailbox by that
name no longer exists.
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Note: This requirement is because a server site can choose to
routinely remove a mailbox with a well-known name (e.g., "system-
alerts") after its contents expire, with the intention of
recreating it when new contents are appropriate.
Example: C: A002 SUBSCRIBE #news.comp.mail.mime
S: A002 OK SUBSCRIBE completed
6.3.7. UNSUBSCRIBE Command
Arguments: mailbox name
Responses: no specific responses for this command
Result: OK - unsubscribe completed
NO - unsubscribe failure: can't unsubscribe that name
BAD - command unknown or arguments invalid
The UNSUBSCRIBE command removes the specified mailbox name from the
server's set of "active" or "subscribed" mailboxes as returned by the
LSUB command. This command returns a tagged OK response only if the
unsubscription is successful.
Example: C: A002 UNSUBSCRIBE #news.comp.mail.mime
S: A002 OK UNSUBSCRIBE completed
6.3.8. LIST Command
Arguments: reference name
mailbox name with possible wildcards
Responses: untagged responses: LIST
Result: OK - list completed
NO - list failure: can't list that reference or name
BAD - command unknown or arguments invalid
The LIST command returns a subset of names from the complete set of
all names available to the client. Zero or more untagged LIST
replies are returned, containing the name attributes, hierarchy
delimiter, and name; see the description of the LIST reply for more
detail.
The LIST command SHOULD return its data quickly, without undue delay.
For example, it SHOULD NOT go to excess trouble to calculate the
\Marked or \Unmarked status or perform other processing; if each name
requires 1 second of processing, then a list of 1200 names would take
20 minutes!
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An empty ("" string) reference name argument indicates that the
mailbox name is interpreted as by SELECT. The returned mailbox names
MUST match the supplied mailbox name pattern. A non-empty reference
name argument is the name of a mailbox or a level of mailbox
hierarchy, and indicates the context in which the mailbox name is
interpreted.
An empty ("" string) mailbox name argument is a special request to
return the hierarchy delimiter and the root name of the name given in
the reference. The value returned as the root MAY be the empty
string if the reference is non-rooted or is an empty string. In all
cases, a hierarchy delimiter (or NIL if there is no hierarchy) is
returned. This permits a client to get the hierarchy delimiter (or
find out that the mailbox names are flat) even when no mailboxes by
that name currently exist.
The reference and mailbox name arguments are interpreted into a
canonical form that represents an unambiguous left-to-right
hierarchy. The returned mailbox names will be in the interpreted
form.
Note: The interpretation of the reference argument is
implementation-defined. It depends upon whether the server
implementation has a concept of the "current working directory"
and leading "break out characters", which override the current
working directory.
For example, on a server which exports a UNIX or NT filesystem,
the reference argument contains the current working directory, and
the mailbox name argument would contain the name as interpreted in
the current working directory.
If a server implementation has no concept of break out characters,
the canonical form is normally the reference name appended with
the mailbox name. Note that if the server implements the
namespace convention (Section 5.1.2), "#" is a break out character
and must be treated as such.
If the reference argument is not a level of mailbox hierarchy
(that is, it is a \NoInferiors name), and/or the reference
argument does not end with the hierarchy delimiter, it is
implementation-dependent how this is interpreted. For example, a
reference of "foo/bar" and mailbox name of "rag/baz" could be
interpreted as "foo/bar/rag/baz", "foo/barrag/baz", or "foo/rag/
baz". A client SHOULD NOT use such a reference argument except at
the explicit request of the user. A hierarchical browser MUST NOT
make any assumptions about server interpretation of the reference
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unless the reference is a level of mailbox hierarchy AND ends with
the hierarchy delimiter.
Any part of the reference argument that is included in the
interpreted form SHOULD prefix the interpreted form. It SHOULD also
be in the same form as the reference name argument. This rule
permits the client to determine if the returned mailbox name is in
the context of the reference argument, or if something about the
mailbox argument overrode the reference argument. Without this rule,
the client would have to have knowledge of the server's naming
semantics including what characters are "breakouts" that override a
naming context.
For example, here are some examples of how references
and mailbox names might be interpreted on a UNIX-based
server:
Reference Mailbox Name Interpretation
------------ ------------ --------------
~smith/Mail/ foo.* ~smith/Mail/foo.*
archive/ % archive/%
#news. comp.mail.* #news.comp.mail.*
~smith/Mail/ /usr/doc/foo /usr/doc/foo
archive/ ~fred/Mail/* ~fred/Mail/*
The first three examples demonstrate interpretations in
the context of the reference argument. Note that
"~smith/Mail" SHOULD NOT be transformed into something
like "/u2/users/smith/Mail", or it would be impossible
for the client to determine that the interpretation was
in the context of the reference.
The character "*" is a wildcard, and matches zero or more characters
at this position. The character "%" is similar to "*", but it does
not match a hierarchy delimiter. If the "%" wildcard is the last
character of a mailbox name argument, matching levels of hierarchy
are also returned. If these levels of hierarchy are not also
selectable mailboxes, they are returned with the \Noselect mailbox
name attribute (see the description of the LIST response for more
details).
Server implementations are permitted to "hide" otherwise accessible
mailboxes from the wildcard characters, by preventing certain
characters or names from matching a wildcard in certain situations.
For example, a UNIX-based server might restrict the interpretation of
"*" so that an initial "/" character does not match.
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The special name INBOX is included in the output from LIST, if INBOX
is supported by this server for this user and if the uppercase string
"INBOX" matches the interpreted reference and mailbox name arguments
with wildcards as described above. The criteria for omitting INBOX
is whether SELECT INBOX will return failure; it is not relevant
whether the user's real INBOX resides on this or some other server.
Example: C: A101 LIST "" ""
S: * LIST (\Noselect) "/" ""
S: A101 OK LIST Completed
C: A102 LIST #news.comp.mail.misc ""
S: * LIST (\Noselect) "." #news.
S: A102 OK LIST Completed
C: A103 LIST /usr/staff/jones ""
S: * LIST (\Noselect) "/" /
S: A103 OK LIST Completed
C: A202 LIST ~/Mail/ %
S: * LIST (\Noselect) "/" ~/Mail/foo
S: * LIST () "/" ~/Mail/meetings
S: A202 OK LIST completed
6.3.9. LSUB Command
Arguments: reference name
mailbox name with possible wildcards
Responses: untagged responses: LSUB
Result: OK - lsub completed
NO - lsub failure: can't list that reference or name
BAD - command unknown or arguments invalid
The LSUB command returns a subset of names from the set of names that
the user has declared as being "active" or "subscribed". Zero or
more untagged LSUB replies are returned. The arguments to LSUB are
in the same form as those for LIST.
The returned untagged LSUB response MAY contain different mailbox
flags from a LIST untagged response. If this should happen, the
flags in the untagged LIST are considered more authoritative.
A special situation occurs when using LSUB with the % wildcard.
Consider what happens if "foo/bar" (with a hierarchy delimiter of
"/") is subscribed but "foo" is not. A "%" wildcard to LSUB must
return foo, not foo/bar, in the LSUB response, and it MUST be flagged
with the \Noselect attribute.
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The server MUST NOT unilaterally remove an existing mailbox name from
the subscription list even if a mailbox by that name no longer
exists.
Example: C: A002 LSUB "#news." "comp.mail.*"
S: * LSUB () "." #news.comp.mail.mime
S: * LSUB () "." #news.comp.mail.misc
S: A002 OK LSUB completed
C: A003 LSUB "#news." "comp.%"
S: * LSUB (\NoSelect) "." #news.comp.mail
S: A003 OK LSUB completed
6.3.10. STATUS Command
Arguments: mailbox name
status data item names
Responses: REQUIRED untagged responses: STATUS
Result: OK - status completed
NO - status failure: no status for that name
BAD - command unknown or arguments invalid
The STATUS command requests the status of the indicated mailbox. It
does not change the currently selected mailbox, nor does it affect
the state of any messages in the queried mailbox (in particular,
STATUS MUST NOT cause messages to lose the \Recent flag).
The STATUS command provides an alternative to opening a second
IMAP4rev1 connection and doing an EXAMINE command on a mailbox to
query that mailbox's status without deselecting the current mailbox
in the first IMAP4rev1 connection.
Unlike the LIST command, the STATUS command is not guaranteed to be
fast in its response. Under certain circumstances, it can be quite
slow. In some implementations, the server is obliged to open the
mailbox read-only internally to obtain certain status information.
Also unlike the LIST command, the STATUS command does not accept
wildcards.
Note: The STATUS command is intended to access the status of
mailboxes other than the currently selected mailbox. Because the
STATUS command can cause the mailbox to be opened internally, and
because this information is available by other means on the
selected mailbox, the STATUS command SHOULD NOT be used on the
currently selected mailbox.
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The STATUS command MUST NOT be used as a "check for new messages
in the selected mailbox" operation (refer to sections 7,
Section 7.3.1, and Section 7.3.2 for more information about the
proper method for new message checking).
Because the STATUS command is not guaranteed to be fast in its
results, clients SHOULD NOT expect to be able to issue many
consecutive STATUS commands and obtain reasonable performance.
The currently defined status data items that can be requested are:
MESSAGES The number of messages in the mailbox.
RECENT The number of messages with the \Recent flag set.
UIDNEXT The next unique identifier value of the mailbox. Refer to
Section 2.3.1.1 for more information.
UIDVALIDITY The unique identifier validity value of the mailbox.
Refer to Section 2.3.1.1 for more information.
UNSEEN The number of messages which do not have the \Seen flag set.
Example: C: A042 STATUS blurdybloop (UIDNEXT MESSAGES)
S: * STATUS blurdybloop (MESSAGES 231 UIDNEXT 44292)
S: A042 OK STATUS completed
6.3.11. APPEND Command
Arguments: mailbox name
OPTIONAL flag parenthesized list
OPTIONAL date/time string
message literal
Responses: no specific responses for this command
Result: OK - append completed
NO - append error: can't append to that mailbox, error
in flags or date/time or message text
BAD - command unknown or arguments invalid
The APPEND command appends the literal argument as a new message to
the end of the specified destination mailbox. This argument SHOULD
be in the format of an [RFC-5322] message. 8-bit characters are
permitted in the message. A server implementation that is unable to
preserve 8-bit data properly MUST be able to reversibly convert 8-bit
APPEND data to 7-bit using a [MIME-IMB] content transfer encoding.
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Note: There may be exceptions, e.g., draft messages, in which
required [RFC-5322] header lines are omitted in the message
literal argument to APPEND. The full implications of doing so
must be understood and carefully weighed.
If a flag parenthesized list is specified, the flags SHOULD be set in
the resulting message; otherwise, the flag list of the resulting
message is set to empty by default. In either case, the Recent flag
is also set.
If a date-time is specified, the internal date SHOULD be set in the
resulting message; otherwise, the internal date of the resulting
message is set to the current date and time by default.
If the append is unsuccessful for any reason, the mailbox MUST be
restored to its state before the APPEND attempt; no partial appending
is permitted.
If the destination mailbox does not exist, a server MUST return an
error, and MUST NOT automatically create the mailbox. Unless it is
certain that the destination mailbox can not be created, the server
MUST send the response code "[TRYCREATE]" as the prefix of the text
of the tagged NO response. This gives a hint to the client that it
can attempt a CREATE command and retry the APPEND if the CREATE is
successful.
If the mailbox is currently selected, the normal new message actions
SHOULD occur. Specifically, the server SHOULD notify the client
immediately via an untagged EXISTS response. If the server does not
do so, the client MAY issue a NOOP command (or failing that, a CHECK
command) after one or more APPEND commands.
Example: C: A003 APPEND saved-messages (\Seen) {310}
S: + Ready for literal data
C: Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST)
C: From: Fred Foobar <foobar@Blurdybloop.COM>
C: Subject: afternoon meeting
C: To: mooch@owatagu.siam.edu
C: Message-Id: <B27397-0100000@Blurdybloop.COM>
C: MIME-Version: 1.0
C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII
C:
C: Hello Joe, do you think we can meet at 3:30 tomorrow?
C:
S: A003 OK APPEND completed
Note: The APPEND command is not used for message delivery, because it
does not provide a mechanism to transfer [SMTP] envelope information.
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6.4. Client Commands - Selected State
In the selected state, commands that manipulate messages in a mailbox
are permitted.
In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT),
and the authenticated state commands (SELECT, EXAMINE, CREATE,
DELETE, RENAME, SUBSCRIBE, UNSUBSCRIBE, LIST, LSUB, STATUS, and
APPEND), the following commands are valid in the selected state:
CHECK, CLOSE, EXPUNGE, SEARCH, FETCH, STORE, COPY, and UID.
6.4.1. CHECK Command
Arguments: none
Responses: no specific responses for this command
Result: OK - check completed
BAD - command unknown or arguments invalid
The CHECK command requests a checkpoint of the currently selected
mailbox. A checkpoint refers to any implementation-dependent
housekeeping associated with the mailbox (e.g., resolving the
server's in-memory state of the mailbox with the state on its disk)
that is not normally executed as part of each command. A checkpoint
MAY take a non-instantaneous amount of real time to complete. If a
server implementation has no such housekeeping considerations, CHECK
is equivalent to NOOP.
There is no guarantee that an EXISTS untagged response will happen as
a result of CHECK. NOOP, not CHECK, SHOULD be used for new message
polling.
Example: C: FXXZ CHECK
S: FXXZ OK CHECK Completed
6.4.2. CLOSE Command
Arguments: none
Responses: no specific responses for this command
Result: OK - close completed, now in authenticated state
BAD - command unknown or arguments invalid
The CLOSE command permanently removes all messages that have the
\Deleted flag set from the currently selected mailbox, and returns to
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the authenticated state from the selected state. No untagged EXPUNGE
responses are sent.
No messages are removed, and no error is given, if the mailbox is
selected by an EXAMINE command or is otherwise selected read-only.
Even if a mailbox is selected, a SELECT, EXAMINE, or LOGOUT command
MAY be issued without previously issuing a CLOSE command. The
SELECT, EXAMINE, and LOGOUT commands implicitly close the currently
selected mailbox without doing an expunge. However, when many
messages are deleted, a CLOSE-LOGOUT or CLOSE-SELECT sequence is
considerably faster than an EXPUNGE-LOGOUT or EXPUNGE-SELECT because
no untagged EXPUNGE responses (which the client would probably
ignore) are sent.
Example: C: A341 CLOSE
S: A341 OK CLOSE completed
6.4.3. EXPUNGE Command
Arguments: none
Responses: untagged responses: EXPUNGE
Result: OK - expunge completed
NO - expunge failure: can't expunge (e.g., permission
denied)
BAD - command unknown or arguments invalid
The EXPUNGE command permanently removes all messages that have the
\Deleted flag set from the currently selected mailbox. Before
returning an OK to the client, an untagged EXPUNGE response is sent
for each message that is removed. Note that if any messages with the
\Recent flag set are expunged, an untagged RECENT response is sent
after the untagged EXPUNGE(s) to update the client's count of RECENT
messages.
Example: C: A202 EXPUNGE
S: * 3 EXPUNGE
S: * 3 EXPUNGE
S: * 5 EXPUNGE
S: * 8 EXPUNGE
S: A202 OK EXPUNGE completed
Note: In this example, messages 3, 4, 7, and 11 had the \Deleted flag
set. See the description of the EXPUNGE response for further
explanation.
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6.4.4. SEARCH Command
Arguments: OPTIONAL [CHARSET] specification
searching criteria (one or more)
Responses: REQUIRED untagged response: SEARCH
Result: OK - search completed
NO - search error: can't search that [CHARSET] or
criteria
BAD - command unknown or arguments invalid
The SEARCH command searches the mailbox for messages that match the
given searching criteria. Searching criteria consist of one or more
search keys. The untagged SEARCH response from the server contains a
listing of message sequence numbers corresponding to those messages
that match the searching criteria.
When multiple keys are specified, the result is the intersection (AND
function) of all the messages that match those keys. For example,
the criteria DELETED FROM "SMITH" SINCE 1-Feb-1994 refers to all
deleted messages from Smith that were placed in the mailbox since
February 1, 1994. A search key can also be a parenthesized list of
one or more search keys (e.g., for use with the OR and NOT keys).
Server implementations MAY exclude [MIME-IMB] body parts with
terminal content media types other than TEXT and MESSAGE from
consideration in SEARCH matching.
The OPTIONAL [CHARSET] specification consists of the word "CHARSET"
followed by a registered [CHARSET]. It indicates the [CHARSET] of
the strings that appear in the search criteria. [MIME-IMB] content
transfer encodings, and [MIME-HDRS] strings in [RFC-5322]/[MIME-IMB]
headers, MUST be decoded before comparing text. US-ASCII MUST be
supported; other [CHARSET]s MAY be supported.
If the server does not support the specified [CHARSET], it MUST
return a tagged NO response (not a BAD). This response SHOULD
contain the BADCHARSET response code, which MAY list the [CHARSET]s
supported by the server.
In all search keys that use strings, a message matches the key if the
string is a substring of the associated text. The matching is case-
insensitive. Note that the empty string is a substring; this is
useful when doing a HEADER search.
The defined search keys are as follows. Refer to the Formal Syntax
section for the precise syntactic definitions of the arguments.
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<sequence set> Messages with message sequence numbers corresponding
to the specified message sequence number set.
ALL All messages in the mailbox; the default initial key for ANDing.
ANSWERED Messages with the \Answered flag set.
BCC <string> Messages that contain the specified string in the
envelope structure's BCC field.
BEFORE <date> Messages whose internal date (disregarding time and
timezone) is earlier than the specified date.
BODY <string> Messages that contain the specified string in the body
of the message.
CC <string> Messages that contain the specified string in the
envelope structure's CC field.
DELETED Messages with the \Deleted flag set.
DRAFT Messages with the \Draft flag set.
FLAGGED Messages with the \Flagged flag set.
FROM <string> Messages that contain the specified string in the
envelope structure's FROM field.
HEADER <field-name> <string> Messages that have a header with the
specified field-name (as defined in [RFC-5322]) and that contains
the specified string in the text of the header (what comes after
the colon). If the string to search is zero-length, this matches
all messages that have a header line with the specified field-name
regardless of the contents.
KEYWORD <flag> Messages with the specified keyword flag set.
LARGER <n> Messages with an [RFC-5322] size larger than the
specified number of octets.
NEW Messages that have the \Recent flag set but not the \Seen flag.
This is functionally equivalent to "(RECENT UNSEEN)".
NOT <search-key> Messages that do not match the specified search
key.
OLD Messages that do not have the \Recent flag set. This is
functionally equivalent to "NOT RECENT" (as opposed to "NOT NEW").
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ON <date> Messages whose internal date (disregarding time and
timezone) is within the specified date.
OR <search-key1> <search-key2> Messages that match either search
key.
RECENT Messages that have the \Recent flag set.
SEEN Messages that have the \Seen flag set.
SENTBEFORE <date> Messages whose [RFC-5322] Date: header
(disregarding time and timezone) is earlier than the specified
date.
SENTON <date> Messages whose [RFC-5322] Date: header (disregarding
time and timezone) is within the specified date.
SENTSINCE <date> Messages whose [RFC-5322] Date: header
(disregarding time and timezone) is within or later than the
specified date.
SINCE <date> Messages whose internal date (disregarding time and
timezone) is within or later than the specified date.
SMALLER <n> Messages with an [RFC-5322] size smaller than the
specified number of octets.
SUBJECT <string> Messages that contain the specified string in the
envelope structure's SUBJECT field.
TEXT <string> Messages that contain the specified string in the
header or body of the message.
TO <string> Messages that contain the specified string in the
envelope structure's TO field.
UID <sequence set> Messages with unique identifiers corresponding to
the specified unique identifier set. Sequence set ranges are
permitted.
UNANSWERED Messages that do not have the \Answered flag set.
UNDELETED Messages that do not have the \Deleted flag set.
UNDRAFT Messages that do not have the \Draft flag set.
UNFLAGGED Messages that do not have the \Flagged flag set.
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UNKEYWORD <flag> Messages that do not have the specified keyword
flag set.
UNSEEN Messages that do not have the \Seen flag set.
Example: C: A282 SEARCH FLAGGED SINCE 1-Feb-1994 NOT FROM "Smith"
S: * SEARCH 2 84 882
S: A282 OK SEARCH completed
C: A283 SEARCH TEXT "string not in mailbox"
S: * SEARCH
S: A283 OK SEARCH completed
C: A284 SEARCH CHARSET UTF-8 TEXT {6}
S: + Ready for literal text
C: XXXXXX
S: * SEARCH 43
S: A284 OK SEARCH completed
Note: Since this document is restricted to 7-bit ASCII text, it is
not possible to show actual UTF-8 data. The "XXXXXX" is a
placeholder for what would be 6 octets of 8-bit data in an actual
transaction.
6.4.5. FETCH Command
Arguments: sequence set
message data item names or macro
Responses: untagged responses: FETCH
Result: OK - fetch completed
NO - fetch error: can't fetch that data
BAD - command unknown or arguments invalid
The FETCH command retrieves data associated with a message in the
mailbox. The data items to be fetched can be either a single atom or
a parenthesized list.
Most data items, identified in the formal syntax under the msg-att-
static rule, are static and MUST NOT change for any particular
message. Other data items, identified in the formal syntax under the
msg-att-dynamic rule, MAY change, either as a result of a STORE
command or due to external events.
For example, if a client receives an ENVELOPE for a message when
it already knows the envelope, it can safely ignore the newly
transmitted envelope.
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There are three macros which specify commonly-used sets of data
items, and can be used instead of data items. A macro must be used
by itself, and not in conjunction with other macros or data items.
ALL Macro equivalent to: (FLAGS INTERNALDATE RFC822.SIZE ENVELOPE)
FAST Macro equivalent to: (FLAGS INTERNALDATE RFC822.SIZE)
FULL Macro equivalent to: (FLAGS INTERNALDATE RFC822.SIZE ENVELOPE
BODY)
The currently defined data items that can be fetched are:
BODY Non-extensible form of BODYSTRUCTURE.
BODY[<section>]<<partial>>
The text of a particular body section. The section
specification is a set of zero or more part specifiers
delimited by periods. A part specifier is either a part number
or one of the following: HEADER, HEADER.FIELDS,
HEADER.FIELDS.NOT, MIME, and TEXT. An empty section
specification refers to the entire message, including the
header.
Every message has at least one part number. Non-[MIME-IMB]
messages, and non-multipart [MIME-IMB] messages with no
encapsulated message, only have a part 1.
Multipart messages are assigned consecutive part numbers, as
they occur in the message. If a particular part is of type
message or multipart, its parts MUST be indicated by a period
followed by the part number within that nested multipart part.
A part of type MESSAGE/RFC822 also has nested part numbers,
referring to parts of the MESSAGE part's body.
The HEADER, HEADER.FIELDS, HEADER.FIELDS.NOT, and TEXT part
specifiers can be the sole part specifier or can be prefixed by
one or more numeric part specifiers, provided that the numeric
part specifier refers to a part of type MESSAGE/RFC822. The
MIME part specifier MUST be prefixed by one or more numeric
part specifiers.
The HEADER, HEADER.FIELDS, and HEADER.FIELDS.NOT part
specifiers refer to the [RFC-5322] header of the message or of
an encapsulated [MIME-IMT] MESSAGE/RFC822 message.
HEADER.FIELDS and HEADER.FIELDS.NOT are followed by a list of
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field-name (as defined in [RFC-5322]) names, and return a
subset of the header. The subset returned by HEADER.FIELDS
contains only those header fields with a field-name that
matches one of the names in the list; similarly, the subset
returned by HEADER.FIELDS.NOT contains only the header fields
with a non-matching field-name. The field-matching is case-
insensitive but otherwise exact. Subsetting does not exclude
the [RFC-5322] delimiting blank line between the header and the
body; the blank line is included in all header fetches, except
in the case of a message which has no body and no blank line.
The MIME part specifier refers to the [MIME-IMB] header for
this part.
The TEXT part specifier refers to the text body of the message,
omitting the [RFC-5322] header.
Here is an example of a complex message with some of its
part specifiers:
HEADER ([RFC-5322] header of the message)
TEXT ([RFC-5322] text body of the message) MULTIPART/MIXED
1 TEXT/PLAIN
2 APPLICATION/OCTET-STREAM
3 MESSAGE/RFC822
3.HEADER ([RFC-5322] header of the message)
3.TEXT ([RFC-5322] text body of the message) MULTIPART/MIXED
3.1 TEXT/PLAIN
3.2 APPLICATION/OCTET-STREAM
4 MULTIPART/MIXED
4.1 IMAGE/GIF
4.1.MIME ([MIME-IMB] header for the IMAGE/GIF)
4.2 MESSAGE/RFC822
4.2.HEADER ([RFC-5322] header of the message)
4.2.TEXT ([RFC-5322] text body of the message) MULTIPART/MIXED
4.2.1 TEXT/PLAIN
4.2.2 MULTIPART/ALTERNATIVE
4.2.2.1 TEXT/PLAIN
4.2.2.2 TEXT/RICHTEXT
It is possible to fetch a substring of the designated text.
This is done by appending an open angle bracket ("<"), the
octet position of the first desired octet, a period, the
maximum number of octets desired, and a close angle bracket
(">") to the part specifier. If the starting octet is beyond
the end of the text, an empty string is returned.
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Any partial fetch that attempts to read beyond the end of the
text is truncated as appropriate. A partial fetch that starts
at octet 0 is returned as a partial fetch, even if this
truncation happened.
Note: This means that BODY[]<0.2048> of a 1500-octet message
will return BODY[]<0> with a literal of size 1500, not
BODY[].
Note: A substring fetch of a HEADER.FIELDS or
HEADER.FIELDS.NOT part specifier is calculated after
subsetting the header.
The \Seen flag is implicitly set; if this causes the flags to
change, they SHOULD be included as part of the FETCH responses.
BODY.PEEK[<section>]<<partial>> An alternate form of BODY[<section>]
that does not implicitly set the \Seen flag.
BODYSTRUCTURE The [MIME-IMB] body structure of the message. This is
computed by the server by parsing the [MIME-IMB] header fields in
the [RFC-5322] header and [MIME-IMB] headers.
ENVELOPE The envelope structure of the message. This is computed by
the server by parsing the [RFC-5322] header into the component
parts, defaulting various fields as necessary.
FLAGS The flags that are set for this message.
INTERNALDATE The internal date of the message.
RFC822 Functionally equivalent to BODY[], differing in the syntax of
the resulting untagged FETCH data (RFC822 is returned).
RFC822.HEADER Functionally equivalent to BODY.PEEK[HEADER],
differing in the syntax of the resulting untagged FETCH data
(RFC822.HEADER is returned).
RFC822.SIZE The [RFC-5322] size of the message.
RFC822.TEXT Functionally equivalent to BODY[TEXT], differing in the
syntax of the resulting untagged FETCH data (RFC822.TEXT is
returned).
UID The unique identifier for the message.
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Example: C: A654 FETCH 2:4 (FLAGS BODY[HEADER.FIELDS (DATE FROM)])
S: * 2 FETCH ....
S: * 3 FETCH ....
S: * 4 FETCH ....
S: A654 OK FETCH completed
6.4.6. STORE Command
Arguments: sequence set
message data item name
value for message data item
Responses: untagged responses: FETCH
Result: OK - store completed
NO - store error: can't store that data
BAD - command unknown or arguments invalid
The STORE command alters data associated with a message in the
mailbox. Normally, STORE will return the updated value of the data
with an untagged FETCH response. A suffix of ".SILENT" in the data
item name prevents the untagged FETCH, and the server SHOULD assume
that the client has determined the updated value itself or does not
care about the updated value.
Note: Regardless of whether or not the ".SILENT" suffix was used,
the server SHOULD send an untagged FETCH response if a change to a
message's flags from an external source is observed. The intent
is that the status of the flags is determinate without a race
condition.
The currently defined data items that can be stored are:
FLAGS <flag list> Replace the flags for the message (other than
\Recent) with the argument. The new value of the flags is
returned as if a FETCH of those flags was done.
FLAGS.SILENT <flag list> Equivalent to FLAGS, but without returning
a new value.
+FLAGS <flag list> Add the argument to the flags for the message.
The new value of the flags is returned as if a FETCH of those
flags was done.
+FLAGS.SILENT <flag list> Equivalent to +FLAGS, but without
returning a new value.
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-FLAGS <flag list> Remove the argument from the flags for the
message. The new value of the flags is returned as if a FETCH of
those flags was done.
-FLAGS.SILENT <flag list> Equivalent to -FLAGS, but without
returning a new value.
Example: C: A003 STORE 2:4 +FLAGS (\Deleted)
S: * 2 FETCH (FLAGS (\Deleted \Seen))
S: * 3 FETCH (FLAGS (\Deleted))
S: * 4 FETCH (FLAGS (\Deleted \Flagged \Seen))
S: A003 OK STORE completed
6.4.7. COPY Command
Arguments: sequence set
mailbox name
Responses: no specific responses for this command
Result: OK - copy completed
NO - copy error: can't copy those messages or to that
name
BAD - command unknown or arguments invalid
The COPY command copies the specified message(s) to the end of the
specified destination mailbox. The flags and internal date of the
message(s) SHOULD be preserved, and the Recent flag SHOULD be set, in
the copy.
If the destination mailbox does not exist, a server SHOULD return an
error. It SHOULD NOT automatically create the mailbox. Unless it is
certain that the destination mailbox can not be created, the server
MUST send the response code "[TRYCREATE]" as the prefix of the text
of the tagged NO response. This gives a hint to the client that it
can attempt a CREATE command and retry the COPY if the CREATE is
successful.
If the COPY command is unsuccessful for any reason, server
implementations MUST restore the destination mailbox to its state
before the COPY attempt.
Example: C: A003 COPY 2:4 MEETING
S: A003 OK COPY completed
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6.4.8. UID Command
Arguments: command name
command arguments
Responses: untagged responses: FETCH, SEARCH
Result: OK - UID command completed
NO - UID command error
BAD - command unknown or arguments invalid
The UID command has two forms. In the first form, it takes as its
arguments a COPY, FETCH, or STORE command with arguments appropriate
for the associated command. However, the numbers in the sequence set
argument are unique identifiers instead of message sequence numbers.
Sequence set ranges are permitted, but there is no guarantee that
unique identifiers will be contiguous.
A non-existent unique identifier is ignored without any error message
generated. Thus, it is possible for a UID FETCH command to return an
OK without any data or a UID COPY or UID STORE to return an OK
without performing any operations.
In the second form, the UID command takes a SEARCH command with
SEARCH command arguments. The interpretation of the arguments is the
same as with SEARCH; however, the numbers returned in a SEARCH
response for a UID SEARCH command are unique identifiers instead of
message sequence numbers. For example, the command UID SEARCH 1:100
UID 443:557 returns the unique identifiers corresponding to the
intersection of two sequence sets, the message sequence number range
1:100 and the UID range 443:557.
Note: in the above example, the UID range 443:557 appears. The
same comment about a non-existent unique identifier being ignored
without any error message also applies here. Hence, even if
neither UID 443 or 557 exist, this range is valid and would
include an existing UID 495.
Also note that a UID range of 559:* always includes the UID of the
last message in the mailbox, even if 559 is higher than any
assigned UID value. This is because the contents of a range are
independent of the order of the range endpoints. Thus, any UID
range with * as one of the endpoints indicates at least one
message (the message with the highest numbered UID), unless the
mailbox is empty.
The number after the "*" in an untagged FETCH response is always a
message sequence number, not a unique identifier, even for a UID
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command response. However, server implementations MUST implicitly
include the UID message data item as part of any FETCH response
caused by a UID command, regardless of whether a UID was specified as
a message data item to the FETCH.
Note: The rule about including the UID message data item as part of a
FETCH response primarily applies to the UID FETCH and UID STORE
commands, including a UID FETCH command that does not include UID as
a message data item. Although it is unlikely that the other UID
commands will cause an untagged FETCH, this rule applies to these
commands as well.
Example: C: A999 UID FETCH 4827313:4828442 FLAGS
S: * 23 FETCH (FLAGS (\Seen) UID 4827313)
S: * 24 FETCH (FLAGS (\Seen) UID 4827943)
S: * 25 FETCH (FLAGS (\Seen) UID 4828442)
S: A999 OK UID FETCH completed
6.5. Client Commands - Experimental/Expansion
6.5.1. X<atom> Command
Arguments: implementation defined
Responses: implementation defined
Result: OK - command completed
NO - failure
BAD - command unknown or arguments invalid
Any command prefixed with an X is an experimental command. Commands
which are not part of this specification, a standard or standards-
track revision of this specification, or an IESG-approved
experimental protocol, MUST use the X prefix.
Any added untagged responses issued by an experimental command MUST
also be prefixed with an X. Server implementations MUST NOT send any
such untagged responses, unless the client requested it by issuing
the associated experimental command.
Example: C: a441 CAPABILITY
S: * CAPABILITY IMAP4rev1 XPIG-LATIN
S: a441 OK CAPABILITY completed
C: A442 XPIG-LATIN
S: * XPIG-LATIN ow-nay eaking-spay ig-pay atin-lay
S: A442 OK XPIG-LATIN ompleted-cay
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7. Server Responses
Server responses are in three forms: status responses, server data,
and command continuation request. The information contained in a
server response, identified by "Contents:" in the response
descriptions below, is described by function, not by syntax. The
precise syntax of server responses is described in the Formal Syntax
section.
The client MUST be prepared to accept any response at all times.
Status responses can be tagged or untagged. Tagged status responses
indicate the completion result (OK, NO, or BAD status) of a client
command, and have a tag matching the command.
Some status responses, and all server data, are untagged. An
untagged response is indicated by the token "*" instead of a tag.
Untagged status responses indicate server greeting, or server status
that does not indicate the completion of a command (for example, an
impending system shutdown alert). For historical reasons, untagged
server data responses are also called "unsolicited data", although
strictly speaking, only unilateral server data is truly
"unsolicited".
Certain server data MUST be recorded by the client when it is
received; this is noted in the description of that data. Such data
conveys critical information which affects the interpretation of all
subsequent commands and responses (e.g., updates reflecting the
creation or destruction of messages).
Other server data SHOULD be recorded for later reference; if the
client does not need to record the data, or if recording the data has
no obvious purpose (e.g., a SEARCH response when no SEARCH command is
in progress), the data SHOULD be ignored.
An example of unilateral untagged server data occurs when the IMAP
connection is in the selected state. In the selected state, the
server checks the mailbox for new messages as part of command
execution. Normally, this is part of the execution of every command;
hence, a NOOP command suffices to check for new messages. If new
messages are found, the server sends untagged EXISTS and RECENT
responses reflecting the new size of the mailbox. Server
implementations that offer multiple simultaneous access to the same
mailbox SHOULD also send appropriate unilateral untagged FETCH and
EXPUNGE responses if another agent changes the state of any message
flags or expunges any messages.
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Command continuation request responses use the token "+" instead of a
tag. These responses are sent by the server to indicate acceptance
of an incomplete client command and readiness for the remainder of
the command.
7.1. Server Responses - Status Responses
Status responses are OK, NO, BAD, PREAUTH and BYE. OK, NO, and BAD
can be tagged or untagged. PREAUTH and BYE are always untagged.
Status responses MAY include an OPTIONAL "response code". A response
code consists of data inside square brackets in the form of an atom,
possibly followed by a space and arguments. The response code
contains additional information or status codes for client software
beyond the OK/NO/BAD condition, and are defined when there is a
specific action that a client can take based upon the additional
information.
The currently defined response codes are:
ALERT The human-readable text contains a special alert that MUST be
presented to the user in a fashion that calls the user's attention
to the message.
BADCHARSET Optionally followed by a parenthesized list of charsets.
A SEARCH failed because the given charset is not supported by this
implementation. If the optional list of charsets is given, this
lists the charsets that are supported by this implementation.
CAPABILITY Followed by a list of capabilities. This can appear in
the initial OK or PREAUTH response to transmit an initial
capabilities list. This makes it unnecessary for a client to send
a separate CAPABILITY command if it recognizes this response.
PARSE The human-readable text represents an error in parsing the
[RFC-5322] header or [MIME-IMB] headers of a message in the
mailbox.
PERMANENTFLAGS Followed by a parenthesized list of flags, indicates
which of the known flags the client can change permanently. Any
flags that are in the FLAGS untagged response, but not the
PERMANENTFLAGS list, can not be set permanently. If the client
attempts to STORE a flag that is not in the PERMANENTFLAGS list,
the server will either ignore the change or store the state change
for the remainder of the current session only. The PERMANENTFLAGS
list can also include the special flag \*, which indicates that it
is possible to create new keywords by attempting to store those
flags in the mailbox.
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READ-ONLY The mailbox is selected read-only, or its access while
selected has changed from read-write to read-only.
READ-WRITE The mailbox is selected read-write, or its access while
selected has changed from read-only to read-write.
TRYCREATE An APPEND or COPY attempt is failing because the target
mailbox does not exist (as opposed to some other reason). This is
a hint to the client that the operation can succeed if the mailbox
is first created by the CREATE command.
UIDNEXT Followed by a decimal number, indicates the next unique
identifier value. Refer to Section 2.3.1.1 for more information.
UIDVALIDITY Followed by a decimal number, indicates the unique
identifier validity value. Refer to Section 2.3.1.1 for more
information.
UNSEEN Followed by a decimal number, indicates the number of the
first message without the \Seen flag set.
Additional response codes defined by particular client or server
implementations SHOULD be prefixed with an "X" until they are added
to a revision of this protocol. Client implementations SHOULD ignore
response codes that they do not recognize.
7.1.1. OK Response
Contents: OPTIONAL response code
human-readable text
The OK response indicates an information message from the server.
When tagged, it indicates successful completion of the associated
command. The human-readable text MAY be presented to the user as an
information message. The untagged form indicates an information-only
message; the nature of the information MAY be indicated by a response
code.
The untagged form is also used as one of three possible greetings at
connection startup. It indicates that the connection is not yet
authenticated and that a LOGIN command is needed.
Example: S: * OK IMAP4rev1 server ready
C: A001 LOGIN fred blurdybloop
S: * OK [ALERT] System shutdown in 10 minutes
S: A001 OK LOGIN Completed
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7.1.2. NO Response
Contents: OPTIONAL response code
human-readable text
The NO response indicates an operational error message from the
server. When tagged, it indicates unsuccessful completion of the
associated command. The untagged form indicates a warning; the
command can still complete successfully. The human-readable text
describes the condition.
Example: C: A222 COPY 1:2 owatagusiam
S: * NO Disk is 98% full, please delete unnecessary data
S: A222 OK COPY completed
C: A223 COPY 3:200 blurdybloop
S: * NO Disk is 98% full, please delete unnecessary data
S: * NO Disk is 99% full, please delete unnecessary data
S: A223 NO COPY failed: disk is full
7.1.3. BAD Response
Contents: OPTIONAL response code
human-readable text
The BAD response indicates an error message from the server. When
tagged, it reports a protocol-level error in the client's command;
the tag indicates the command that caused the error. The untagged
form indicates a protocol-level error for which the associated
command can not be determined; it can also indicate an internal
server failure. The human-readable text describes the condition.
Example: C: ...very long command line...
S: * BAD Command line too long
C: ...empty line...
S: * BAD Empty command line
C: A443 EXPUNGE
S: * BAD Disk crash, attempting salvage to a new disk!
S: * OK Salvage successful, no data lost
S: A443 OK Expunge completed
7.1.4. PREAUTH Response
Contents: OPTIONAL response code
human-readable text
The PREAUTH response is always untagged, and is one of three possible
greetings at connection startup. It indicates that the connection
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has already been authenticated by external means; thus no LOGIN
command is needed.
Example: S: * PREAUTH IMAP4rev1 server logged in as Smith
7.1.5. BYE Response
Contents: OPTIONAL response code
human-readable text
The BYE response is always untagged, and indicates that the server is
about to close the connection. The human-readable text MAY be
displayed to the user in a status report by the client. The BYE
response is sent under one of four conditions:
1. as part of a normal logout sequence. The server will close the
connection after sending the tagged OK response to the LOGOUT
command.
2. as a panic shutdown announcement. The server closes the
connection immediately.
3. as an announcement of an inactivity autologout. The server
closes the connection immediately.
4. as one of three possible greetings at connection startup,
indicating that the server is not willing to accept a connection
from this client. The server closes the connection immediately.
The difference between a BYE that occurs as part of a normal LOGOUT
sequence (the first case) and a BYE that occurs because of a failure
(the other three cases) is that the connection closes immediately in
the failure case. In all cases the client SHOULD continue to read
response data from the server until the connection is closed; this
will ensure that any pending untagged or completion responses are
read and processed.
Example: S: * BYE Autologout; idle for too long
7.2. Server Responses - Server and Mailbox Status
These responses are always untagged. This is how server and mailbox
status data are transmitted from the server to the client. Many of
these responses typically result from a command with the same name.
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7.2.1. CAPABILITY Response
Contents: capability listing
The CAPABILITY response occurs as a result of a CAPABILITY command.
The capability listing contains a space-separated listing of
capability names that the server supports. The capability listing
MUST include the atom "IMAP4rev1".
In addition, client and server implementations MUST implement the
STARTTLS, LOGINDISABLED, and AUTH=PLAIN (described in [PLAIN])
capabilities. See the Security Considerations section for important
information.
A capability name which begins with "AUTH=" indicates that the server
supports that particular authentication mechanism.
The LOGINDISABLED capability indicates that the LOGIN command is
disabled, and that the server will respond with a tagged NO response
to any attempt to use the LOGIN command even if the user name and
password are valid. An IMAP client MUST NOT issue the LOGIN command
if the server advertises the LOGINDISABLED capability.
Other capability names indicate that the server supports an
extension, revision, or amendment to the IMAP4rev1 protocol. Server
responses MUST conform to this document until the client issues a
command that uses the associated capability.
Capability names MUST either begin with "X" or be standard or
standards-track IMAP4rev1 extensions, revisions, or amendments
registered with IANA. A server MUST NOT offer unregistered or non-
standard capability names, unless such names are prefixed with an
"X".
Client implementations SHOULD NOT require any capability name other
than "IMAP4rev1", and MUST ignore any unknown capability names.
A server MAY send capabilities automatically, by using the CAPABILITY
response code in the initial PREAUTH or OK responses, and by sending
an updated CAPABILITY response code in the tagged OK response as part
of a successful authentication. It is unnecessary for a client to
send a separate CAPABILITY command if it recognizes these automatic
capabilities.
Example: S: * CAPABILITY IMAP4rev1 STARTTLS AUTH=GSSAPI XPIG-LATIN
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7.2.2. LIST Response
Contents: name attributes
hierarchy delimiter
name
The LIST response occurs as a result of a LIST command. It returns a
single name that matches the LIST specification. There can be
multiple LIST responses for a single LIST command.
Four name attributes are defined:
\Noinferiors It is not possible for any child levels of hierarchy to
exist under this name; no child levels exist now and none can be
created in the future.
\Noselect It is not possible to use this name as a selectable
mailbox.
\Marked The mailbox has been marked "interesting" by the server; the
mailbox probably contains messages that have been added since the
last time the mailbox was selected.
\Unmarked The mailbox does not contain any additional messages since
the last time the mailbox was selected.
If it is not feasible for the server to determine whether or not the
mailbox is "interesting", the server SHOULD NOT send either \Marked
or \Unmarked. The server MUST NOT send more than one of \Marked,
\Unmarked, and \Noselect for a single mailbox, and MAY send none of
these.
The hierarchy delimiter is a character used to delimit levels of
hierarchy in a mailbox name. A client can use it to create child
mailboxes, and to search higher or lower levels of naming hierarchy.
All children of a top-level hierarchy node MUST use the same
separator character. A NIL hierarchy delimiter means that no
hierarchy exists; the name is a "flat" name.
The name represents an unambiguous left-to-right hierarchy, and MUST
be valid for use as a reference in LIST and LSUB commands. Unless
\Noselect is indicated, the name MUST also be valid as an argument
for commands, such as SELECT, that accept mailbox names.
Example: S: * LIST (\Noselect) "/" ~/Mail/foo
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7.2.3. LSUB Response
Contents: name attributes
hierarchy delimiter
name
The LSUB response occurs as a result of an LSUB command. It returns
a single name that matches the LSUB specification. There can be
multiple LSUB responses for a single LSUB command. The data is
identical in format to the LIST response.
Example: S: * LSUB () "." #news.comp.mail.misc
7.2.4. STATUS Response
Contents: name
status parenthesized list
The STATUS response occurs as a result of an STATUS command. It
returns the mailbox name that matches the STATUS specification and
the requested mailbox status information.
Example: S: * STATUS blurdybloop (MESSAGES 231 UIDNEXT 44292)
7.2.5. SEARCH Response
Contents: zero or more numbers
The SEARCH response occurs as a result of a SEARCH or UID SEARCH
command. The number(s) refer to those messages that match the search
criteria. For SEARCH, these are message sequence numbers; for UID
SEARCH, these are unique identifiers. Each number is delimited by a
space.
Example: S: * SEARCH 2 3 6
7.2.6. FLAGS Response
Contents: flag parenthesized list
The FLAGS response occurs as a result of a SELECT or EXAMINE command.
The flag parenthesized list identifies the flags (at a minimum, the
system-defined flags) that are applicable for this mailbox. Flags
other than the system flags can also exist, depending on server
implementation.
The update from the FLAGS response MUST be recorded by the client.
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Example: S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
7.3. Server Responses - Mailbox Size
These responses are always untagged. This is how changes in the size
of the mailbox are transmitted from the server to the client.
Immediately following the "*" token is a number that represents a
message count.
7.3.1. EXISTS Response
Contents: none
The EXISTS response reports the number of messages in the mailbox.
This response occurs as a result of a SELECT or EXAMINE command, and
if the size of the mailbox changes (e.g., new messages).
The update from the EXISTS response MUST be recorded by the client.
Example: S: * 23 EXISTS
7.3.2. RECENT Response
Contents: none
The RECENT response reports the number of messages with the \Recent
flag set. This response occurs as a result of a SELECT or EXAMINE
command, and if the size of the mailbox changes (e.g., new messages).
Note: It is not guaranteed that the message sequence numbers of
recent messages will be a contiguous range of the highest n
messages in the mailbox (where n is the value reported by the
RECENT response). Examples of situations in which this is not the
case are: multiple clients having the same mailbox open (the first
session to be notified will see it as recent, others will probably
see it as non-recent), and when the mailbox is re-ordered by a
non-IMAP agent.
The only reliable way to identify recent messages is to look at
message flags to see which have the \Recent flag set, or to do a
SEARCH RECENT.
The update from the RECENT response MUST be recorded by the client.
Example: S: * 5 RECENT
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7.4. Server Responses - Message Status
These responses are always untagged. This is how message data are
transmitted from the server to the client, often as a result of a
command with the same name. Immediately following the "*" token is a
number that represents a message sequence number.
7.4.1. EXPUNGE Response
Contents: none
The EXPUNGE response reports that the specified message sequence
number has been permanently removed from the mailbox. The message
sequence number for each successive message in the mailbox is
immediately decremented by 1, and this decrement is reflected in
message sequence numbers in subsequent responses (including other
untagged EXPUNGE responses).
The EXPUNGE response also decrements the number of messages in the
mailbox; it is not necessary to send an EXISTS response with the new
value.
As a result of the immediate decrement rule, message sequence numbers
that appear in a set of successive EXPUNGE responses depend upon
whether the messages are removed starting from lower numbers to
higher numbers, or from higher numbers to lower numbers. For
example, if the last 5 messages in a 9-message mailbox are expunged,
a "lower to higher" server will send five untagged EXPUNGE responses
for message sequence number 5, whereas a "higher to lower server"
will send successive untagged EXPUNGE responses for message sequence
numbers 9, 8, 7, 6, and 5.
An EXPUNGE response MUST NOT be sent when no command is in progress,
nor while responding to a FETCH, STORE, or SEARCH command. This rule
is necessary to prevent a loss of synchronization of message sequence
numbers between client and server. A command is not "in progress"
until the complete command has been received; in particular, a
command is not "in progress" during the negotiation of command
continuation.
Note: UID FETCH, UID STORE, and UID SEARCH are different commands
from FETCH, STORE, and SEARCH. An EXPUNGE response MAY be sent
during a UID command.
The update from the EXPUNGE response MUST be recorded by the client.
Example: S: * 44 EXPUNGE
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7.4.2. FETCH Response
Contents: message data
The FETCH response returns data about a message to the client. The
data are pairs of data item names and their values in parentheses.
This response occurs as the result of a FETCH or STORE command, as
well as by unilateral server decision (e.g., flag updates).
The current data items are:
BODY A form of BODYSTRUCTURE without extension data.
BODY[<section>]<<origin octet>>
A string expressing the body contents of the specified section.
The string SHOULD be interpreted by the client according to the
content transfer encoding, body type, and subtype.
If the origin octet is specified, this string is a substring of
the entire body contents, starting at that origin octet. This
means that BODY[]<0> MAY be truncated, but BODY[] is NEVER
truncated.
Note: The origin octet facility MUST NOT be used by a server
in a FETCH response unless the client specifically requested
it by means of a FETCH of a BODY[<section>]<<partial>> data
item.
8-bit textual data is permitted if a [CHARSET] identifier is
part of the body parameter parenthesized list for this section.
Note that headers (part specifiers HEADER or MIME, or the
header portion of a MESSAGE/RFC822 part), MUST be 7-bit; 8-bit
characters are not permitted in headers. Note also that the
[RFC-5322] delimiting blank line between the header and the
body is not affected by header line subsetting; the blank line
is always included as part of header data, except in the case
of a message which has no body and no blank line.
Non-textual data such as binary data MUST be transfer encoded
into a textual form, such as BASE64, prior to being sent to the
client. To derive the original binary data, the client MUST
decode the transfer encoded string.
BODYSTRUCTURE
A parenthesized list that describes the [MIME-IMB] body
structure of a message. This is computed by the server by
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parsing the [MIME-IMB] header fields, defaulting various fields
as necessary.
For example, a simple text message of 48 lines and 2279 octets
can have a body structure of: ("TEXT" "PLAIN" ("CHARSET" "US-
ASCII") NIL NIL "7BIT" 2279 48)
Multiple parts are indicated by parenthesis nesting. Instead
of a body type as the first element of the parenthesized list,
there is a sequence of one or more nested body structures. The
second element of the parenthesized list is the multipart
subtype (mixed, digest, parallel, alternative, etc.).
For example, a two part message consisting of a text and a
BASE64-encoded text attachment can have a body structure of:
(("TEXT" "PLAIN" ("CHARSET" "US-ASCII") NIL NIL "7BIT" 1152
23)("TEXT" "PLAIN" ("CHARSET" "US-ASCII" "NAME" "cc.diff")
"<960723163407.20117h@cac.washington.edu>" "Compiler diff"
"BASE64" 4554 73) "MIXED")
Extension data follows the multipart subtype. Extension data
is never returned with the BODY fetch, but can be returned with
a BODYSTRUCTURE fetch. Extension data, if present, MUST be in
the defined order. The extension data of a multipart body part
are in the following order:
body parameter parenthesized list A parenthesized list of
attribute/value pairs [e.g., ("foo" "bar" "baz" "rag") where
"bar" is the value of "foo", and "rag" is the value of
"baz"] as defined in [MIME-IMB].
body disposition A parenthesized list, consisting of a
disposition type string, followed by a parenthesized list of
disposition attribute/value pairs as defined in
[DISPOSITION].
body language A string or parenthesized list giving the body
language value as defined in [LANGUAGE-TAGS].
body location A string giving the body content URI as defined
in [LOCATION].
Any following extension data are not yet defined in this
version of the protocol. Such extension data can consist of
zero or more NILs, strings, numbers, or potentially nested
parenthesized lists of such data. Client implementations that
do a BODYSTRUCTURE fetch MUST be prepared to accept such
extension data. Server implementations MUST NOT send such
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extension data until it has been defined by a revision of this
protocol.
The basic fields of a non-multipart body part are in the
following order:
body type A string giving the content media type name as
defined in [MIME-IMB].
body subtype A string giving the content subtype name as
defined in [MIME-IMB].
body parameter parenthesized list A parenthesized list of
attribute/value pairs [e.g., ("foo" "bar" "baz" "rag") where
"bar" is the value of "foo" and "rag" is the value of "baz"]
as defined in [MIME-IMB].
body id A string giving the content id as defined in
[MIME-IMB].
body description A string giving the content description as
defined in [MIME-IMB].
body encoding A string giving the content transfer encoding as
defined in [MIME-IMB].
body size A number giving the size of the body in octets.
Note that this size is the size in its transfer encoding and
not the resulting size after any decoding.
A body type of type MESSAGE and subtype RFC822 contains,
immediately after the basic fields, the envelope structure,
body structure, and size in text lines of the encapsulated
message.
A body type of type TEXT contains, immediately after the basic
fields, the size of the body in text lines. Note that this
size is the size in its content transfer encoding and not the
resulting size after any decoding.
Extension data follows the basic fields and the type-specific
fields listed above. Extension data is never returned with the
BODY fetch, but can be returned with a BODYSTRUCTURE fetch.
Extension data, if present, MUST be in the defined order.
The extension data of a non-multipart body part are in the
following order:
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body MD5 A string giving the body MD5 value as defined in
[MD5].
body disposition A parenthesized list with the same content
and function as the body disposition for a multipart body
part.
body language A string or parenthesized list giving the body
language value as defined in [LANGUAGE-TAGS].
body location A string giving the body content URI as defined
in [LOCATION].
Any following extension data are not yet defined in this
version of the protocol, and would be as described above under
multipart extension data.
ENVELOPE
A parenthesized list that describes the envelope structure of a
message. This is computed by the server by parsing the
[RFC-5322] header into the component parts, defaulting various
fields as necessary.
The fields of the envelope structure are in the following
order: date, subject, from, sender, reply-to, to, cc, bcc, in-
reply-to, and message-id. The date, subject, in-reply-to, and
message-id fields are strings. The from, sender, reply-to, to,
cc, and bcc fields are parenthesized lists of address
structures.
An address structure is a parenthesized list that describes an
electronic mail address. The fields of an address structure
are in the following order: personal name, [SMTP] at-domain-
list (source route), mailbox name, and host name.
[RFC-5322] group syntax is indicated by a special form of
address structure in which the host name field is NIL. If the
mailbox name field is also NIL, this is an end of group marker
(semi-colon in RFC 822 syntax). If the mailbox name field is
non-NIL, this is a start of group marker, and the mailbox name
field holds the group name phrase.
If the Date, Subject, In-Reply-To, and Message-ID header lines
are absent in the [RFC-5322] header, the corresponding member
of the envelope is NIL; if these header lines are present but
empty the corresponding member of the envelope is the empty
string.
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Note: some servers may return a NIL envelope member in the
"present but empty" case. Clients SHOULD treat NIL and
empty string as identical.
Note: [RFC-5322] requires that all messages have a valid
Date header. Therefore, the date member in the envelope can
not be NIL or the empty string.
Note: [RFC-5322] requires that the In-Reply-To and Message-
ID headers, if present, have non-empty content. Therefore,
the in-reply-to and message-id members in the envelope can
not be the empty string.
If the From, To, Cc, and Bcc header lines are absent in the
[RFC-5322] header, or are present but empty, the corresponding
member of the envelope is NIL.
If the Sender or Reply-To lines are absent in the [RFC-5322]
header, or are present but empty, the server sets the
corresponding member of the envelope to be the same value as
the from member (the client is not expected to know to do
this).
Note: [RFC-5322] requires that all messages have a valid
From header. Therefore, the from, sender, and reply-to
members in the envelope can not be NIL.
FLAGS A parenthesized list of flags that are set for this message.
INTERNALDATE A string representing the internal date of the message.
RFC822 Equivalent to BODY[].
RFC822.HEADER Equivalent to BODY[HEADER]. Note that this did not
result in \Seen being set, because RFC822.HEADER response data
occurs as a result of a FETCH of RFC822.HEADER. BODY[HEADER]
response data occurs as a result of a FETCH of BODY[HEADER] (which
sets \Seen) or BODY.PEEK[HEADER] (which does not set \Seen).
RFC822.SIZE A number expressing the [RFC-5322] size of the message.
RFC822.TEXT Equivalent to BODY[TEXT].
UID A number expressing the unique identifier of the message.
Example: S: * 23 FETCH (FLAGS (\Seen) RFC822.SIZE 44827)
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7.5. Server Responses - Command Continuation Request
The command continuation request response is indicated by a "+" token
instead of a tag. This form of response indicates that the server is
ready to accept the continuation of a command from the client. The
remainder of this response is a line of text.
This response is used in the AUTHENTICATE command to transmit server
data to the client, and request additional client data. This
response is also used if an argument to any command is a literal.
The client is not permitted to send the octets of the literal unless
the server indicates that it is expected. This permits the server to
process commands and reject errors on a line-by-line basis. The
remainder of the command, including the CRLF that terminates a
command, follows the octets of the literal. If there are any
additional command arguments, the literal octets are followed by a
space and those arguments.
Example: C: A001 LOGIN {11}
S: + Ready for additional command text
C: FRED FOOBAR {7}
S: + Ready for additional command text
C: fat man
S: A001 OK LOGIN completed
C: A044 BLURDYBLOOP {102856}
S: A044 BAD No such command as "BLURDYBLOOP"
8. Sample IMAP4rev1 connection
The following is a transcript of an IMAP4rev1 connection. A long
line in this sample is broken for editorial clarity.
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S: * OK IMAP4rev1 Service Ready
C: a001 login mrc secret
S: a001 OK LOGIN completed
C: a002 select inbox
S: * 18 EXISTS
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
S: * 2 RECENT
S: * OK [UNSEEN 17] Message 17 is the first unseen message
S: * OK [UIDVALIDITY 3857529045] UIDs valid
S: a002 OK [READ-WRITE] SELECT completed
C: a003 fetch 12 full
S: * 12 FETCH (FLAGS (\Seen) INTERNALDATE "17-Jul-1996 02:44:25 -0700"
RFC822.SIZE 4286 ENVELOPE ("Wed, 17 Jul 1996 02:23:25 -0700 (PDT)"
"IMAP4rev1 WG mtg summary and minutes"
(("Terry Gray" NIL "gray" "cac.washington.edu"))
(("Terry Gray" NIL "gray" "cac.washington.edu"))
(("Terry Gray" NIL "gray" "cac.washington.edu"))
((NIL NIL "imap" "cac.washington.edu"))
((NIL NIL "minutes" "CNRI.Reston.VA.US")
("John Klensin" NIL "KLENSIN" "MIT.EDU")) NIL NIL
"<B27397-0100000@cac.washington.edu>")
BODY ("TEXT" "PLAIN" ("CHARSET" "US-ASCII") NIL NIL "7BIT" 3028
92))
S: a003 OK FETCH completed
C: a004 fetch 12 body[header]
S: * 12 FETCH (BODY[HEADER] {342}
S: Date: Wed, 17 Jul 1996 02:23:25 -0700 (PDT)
S: From: Terry Gray <gray@cac.washington.edu>
S: Subject: IMAP4rev1 WG mtg summary and minutes
S: To: imap@cac.washington.edu
S: cc: minutes@CNRI.Reston.VA.US, John Klensin <KLENSIN@MIT.EDU>
S: Message-Id: <B27397-0100000@cac.washington.edu>
S: MIME-Version: 1.0
S: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII
S:
S: )
S: a004 OK FETCH completed
C: a005 store 12 +flags \deleted
S: * 12 FETCH (FLAGS (\Seen \Deleted))
S: a005 OK +FLAGS completed
C: a006 logout
S: * BYE IMAP4rev1 server terminating connection
S: a006 OK LOGOUT completed
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9. Formal Syntax
The following syntax specification uses the Augmented Backus-Naur
Form (ABNF) notation as specified in [ABNF].
In the case of alternative or optional rules in which a later rule
overlaps an earlier rule, the rule which is listed earlier MUST take
priority. For example, "\Seen" when parsed as a flag is the \Seen
flag name and not a flag-extension, even though "\Seen" can be parsed
as a flag-extension. Some, but not all, instances of this rule are
noted below.
Note: [ABNF] rules MUST be followed strictly; in particular:
(1) Except as noted otherwise, all alphabetic characters are case-
insensitive. The use of upper or lower case characters to define
token strings is for editorial clarity only. Implementations MUST
accept these strings in a case-insensitive fashion.
(2) In all cases, SP refers to exactly one space. It is NOT
permitted to substitute TAB, insert additional spaces, or
otherwise treat SP as being equivalent to LWSP.
(3) The ASCII NUL character, %x00, MUST NOT be used at any time.
address = "(" addr-name SP addr-adl SP addr-mailbox SP
addr-host ")"
addr-adl = nstring
; Holds route from [RFC-5322] route-addr if
; non-NIL
addr-host = nstring
; NIL indicates [RFC-5322] group syntax.
; Otherwise, holds [RFC-5322] domain name
addr-mailbox = nstring
; NIL indicates end of [RFC-5322] group; if
; non-NIL and addr-host is NIL, holds
; [RFC-5322] group name.
; Otherwise, holds [RFC-5322] local-part
; after removing [RFC-5322] quoting
addr-name = nstring
; If non-NIL, holds phrase from [RFC-5322]
; mailbox after removing [RFC-5322] quoting
append = "APPEND" SP mailbox [SP flag-list] [SP date-time] SP
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literal
astring = 1*ASTRING-CHAR / string
ASTRING-CHAR = ATOM-CHAR / resp-specials
atom = 1*ATOM-CHAR
ATOM-CHAR = <any CHAR except atom-specials>
atom-specials = "(" / ")" / "{" / SP / CTL / list-wildcards /
quoted-specials / resp-specials
authenticate = "AUTHENTICATE" SP auth-type *(CRLF base64)
auth-type = atom
; Defined by [SASL]
base64 = *(4base64-char) [base64-terminal]
base64-char = ALPHA / DIGIT / "+" / "/"
; Case-sensitive
base64-terminal = (2base64-char "==") / (3base64-char "=")
body = "(" (body-type-1part / body-type-mpart) ")"
body-extension = nstring / number /
"(" body-extension *(SP body-extension) ")"
; Future expansion. Client implementations
; MUST accept body-extension fields. Server
; implementations MUST NOT generate
; body-extension fields except as defined by
; future standard or standards-track
; revisions of this specification.
body-ext-1part = body-fld-md5 [SP body-fld-dsp [SP body-fld-lang
[SP body-fld-loc *(SP body-extension)]]]
; MUST NOT be returned on non-extensible
; "BODY" fetch
body-ext-mpart = body-fld-param [SP body-fld-dsp [SP body-fld-lang
[SP body-fld-loc *(SP body-extension)]]]
; MUST NOT be returned on non-extensible
; "BODY" fetch
body-fields = body-fld-param SP body-fld-id SP body-fld-desc SP
body-fld-enc SP body-fld-octets
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body-fld-desc = nstring
body-fld-dsp = "(" string SP body-fld-param ")" / nil
body-fld-enc = (DQUOTE ("7BIT" / "8BIT" / "BINARY" / "BASE64"/
"QUOTED-PRINTABLE") DQUOTE) / string
body-fld-id = nstring
body-fld-lang = nstring / "(" string *(SP string) ")"
body-fld-loc = nstring
body-fld-lines = number
body-fld-md5 = nstring
body-fld-octets = number
body-fld-param = "(" string SP string *(SP string SP string) ")" / nil
body-type-1part = (body-type-basic / body-type-msg / body-type-text)
[SP body-ext-1part]
body-type-basic = media-basic SP body-fields
; MESSAGE subtype MUST NOT be "RFC822"
body-type-mpart = 1*body SP media-subtype
[SP body-ext-mpart]
body-type-msg = media-message SP body-fields SP envelope
SP body SP body-fld-lines
body-type-text = media-text SP body-fields SP body-fld-lines
capability = ("AUTH=" auth-type) / atom
; New capabilities MUST begin with "X" or be
; registered with IANA as standard or
; standards-track
capability-data = "CAPABILITY" *(SP capability) SP "IMAP4rev1"
*(SP capability)
; Servers MUST implement the STARTTLS, AUTH=PLAIN,
; and LOGINDISABLED capabilities
; Servers which offer RFC 1730 compatibility MUST
; list "IMAP4" as the first capability.
CHAR8 = %x01-ff
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; any OCTET except NUL, %x00
charset = atom / quoted
command = tag SP (command-any / command-auth / command-nonauth /
command-select) CRLF
; Modal based on state
command-any = "CAPABILITY" / "LOGOUT" / "NOOP" / x-command
; Valid in all states
command-auth = append / create / delete / examine / list / lsub /
rename / select / status / subscribe / unsubscribe
; Valid only in Authenticated or Selected state
command-nonauth = login / authenticate / "STARTTLS"
; Valid only when in Not Authenticated state
command-select = "CHECK" / "CLOSE" / "EXPUNGE" / copy / fetch / store /
uid / search
; Valid only when in Selected state
continue-req = "+" SP (resp-text / base64) CRLF
copy = "COPY" SP sequence-set SP mailbox
create = "CREATE" SP mailbox
; Use of INBOX gives a NO error
date = date-text / DQUOTE date-text DQUOTE
date-day = 1*2DIGIT
; Day of month
date-day-fixed = (SP DIGIT) / 2DIGIT
; Fixed-format version of date-day
date-month = "Jan" / "Feb" / "Mar" / "Apr" / "May" / "Jun" /
"Jul" / "Aug" / "Sep" / "Oct" / "Nov" / "Dec"
date-text = date-day "-" date-month "-" date-year
date-year = 4DIGIT
date-time = DQUOTE date-day-fixed "-" date-month "-" date-year
SP time SP zone DQUOTE
delete = "DELETE" SP mailbox
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; Use of INBOX gives a NO error
digit-nz = %x31-39
; 1-9
envelope = "(" env-date SP env-subject SP env-from SP
env-sender SP env-reply-to SP env-to SP env-cc SP
env-bcc SP env-in-reply-to SP env-message-id ")"
env-bcc = "(" 1*address ")" / nil
env-cc = "(" 1*address ")" / nil
env-date = nstring
env-from = "(" 1*address ")" / nil
env-in-reply-to = nstring
env-message-id = nstring
env-reply-to = "(" 1*address ")" / nil
env-sender = "(" 1*address ")" / nil
env-subject = nstring
env-to = "(" 1*address ")" / nil
examine = "EXAMINE" SP mailbox
fetch = "FETCH" SP sequence-set SP ("ALL" / "FULL" / "FAST" /
fetch-att / "(" fetch-att *(SP fetch-att) ")")
fetch-att = "ENVELOPE" / "FLAGS" / "INTERNALDATE" /
"RFC822" [".HEADER" / ".SIZE" / ".TEXT"] /
"BODY" ["STRUCTURE"] / "UID" /
"BODY" section ["<" number "." nz-number ">"] /
"BODY.PEEK" section ["<" number "." nz-number ">"]
flag = "\Answered" / "\Flagged" / "\Deleted" /
"\Seen" / "\Draft" / flag-keyword / flag-extension
; Does not include "\Recent"
flag-extension = "\" atom
; Future expansion. Client implementations
; MUST accept flag-extension flags. Server
; implementations MUST NOT generate
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; flag-extension flags except as defined by
; future standard or standards-track
; revisions of this specification.
flag-fetch = flag / "\Recent"
flag-keyword = atom
flag-list = "(" [flag *(SP flag)] ")"
flag-perm = flag / "\*"
greeting = "*" SP (resp-cond-auth / resp-cond-bye) CRLF
header-fld-name = astring
header-list = "(" header-fld-name *(SP header-fld-name) ")"
list = "LIST" SP mailbox SP list-mailbox
list-mailbox = 1*list-char / string
list-char = ATOM-CHAR / list-wildcards / resp-specials
list-wildcards = "%" / "*"
literal = "{" number "}" CRLF *CHAR8
; Number represents the number of CHAR8s
login = "LOGIN" SP userid SP password
lsub = "LSUB" SP mailbox SP list-mailbox
mailbox = "INBOX" / astring
; INBOX is case-insensitive. All case variants of
; INBOX (e.g., "iNbOx") MUST be interpreted as INBOX
; not as an astring. An astring which consists of
; the case-insensitive sequence "I" "N" "B" "O" "X"
; is considered to be INBOX and not an astring.
; Refer to section 5.1 for further
; semantic details of mailbox names.
mailbox-data = "FLAGS" SP flag-list / "LIST" SP mailbox-list /
"LSUB" SP mailbox-list / "SEARCH" *(SP nz-number) /
"STATUS" SP mailbox SP "(" [status-att-list] ")" /
number SP "EXISTS" / number SP "RECENT"
mailbox-list = "(" [mbx-list-flags] ")" SP
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(DQUOTE QUOTED-CHAR DQUOTE / nil) SP mailbox
mbx-list-flags = *(mbx-list-oflag SP) mbx-list-sflag
*(SP mbx-list-oflag) /
mbx-list-oflag *(SP mbx-list-oflag)
mbx-list-oflag = "\Noinferiors" / flag-extension
; Other flags; multiple possible per LIST response
mbx-list-sflag = "\Noselect" / "\Marked" / "\Unmarked"
; Selectability flags; only one per LIST response
media-basic = ((DQUOTE ("APPLICATION" / "AUDIO" / "IMAGE" /
"MESSAGE" / "VIDEO") DQUOTE) / string) SP
media-subtype
; Defined in [MIME-IMT]
media-message = DQUOTE "MESSAGE" DQUOTE SP DQUOTE "RFC822" DQUOTE
; Defined in [MIME-IMT]
media-subtype = string
; Defined in [MIME-IMT]
media-text = DQUOTE "TEXT" DQUOTE SP media-subtype
; Defined in [MIME-IMT]
message-data = nz-number SP ("EXPUNGE" / ("FETCH" SP msg-att))
msg-att = "(" (msg-att-dynamic / msg-att-static)
*(SP (msg-att-dynamic / msg-att-static)) ")"
msg-att-dynamic = "FLAGS" SP "(" [flag-fetch *(SP flag-fetch)] ")"
; MAY change for a message
msg-att-static = "ENVELOPE" SP envelope / "INTERNALDATE" SP date-time /
"RFC822" [".HEADER" / ".TEXT"] SP nstring /
"RFC822.SIZE" SP number /
"BODY" ["STRUCTURE"] SP body /
"BODY" section ["<" number ">"] SP nstring /
"UID" SP uniqueid
; MUST NOT change for a message
nil = "NIL"
nstring = string / nil
number = 1*DIGIT
; Unsigned 32-bit integer
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; (0 <= n < 4,294,967,296)
nz-number = digit-nz *DIGIT
; Non-zero unsigned 32-bit integer
; (0 < n < 4,294,967,296)
password = astring
quoted = DQUOTE *QUOTED-CHAR DQUOTE
QUOTED-CHAR = <any TEXT-CHAR except quoted-specials> /
"\" quoted-specials
quoted-specials = DQUOTE / "\"
rename = "RENAME" SP mailbox SP mailbox
; Use of INBOX as a destination gives a NO error
response = *(continue-req / response-data) response-done
response-data = "*" SP (resp-cond-state / resp-cond-bye /
mailbox-data / message-data / capability-data) CRLF
response-done = response-tagged / response-fatal
response-fatal = "*" SP resp-cond-bye CRLF
; Server closes connection immediately
response-tagged = tag SP resp-cond-state CRLF
resp-cond-auth = ("OK" / "PREAUTH") SP resp-text
; Authentication condition
resp-cond-bye = "BYE" SP resp-text
resp-cond-state = ("OK" / "NO" / "BAD") SP resp-text
; Status condition
resp-specials = "]"
resp-text = ["[" resp-text-code "]" SP] text
resp-text-code = "ALERT" /
"BADCHARSET" [SP "(" charset *(SP charset) ")" ] /
capability-data / "PARSE" /
"PERMANENTFLAGS" SP "("
[flag-perm *(SP flag-perm)] ")" /
"READ-ONLY" / "READ-WRITE" / "TRYCREATE" /
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"UIDNEXT" SP nz-number / "UIDVALIDITY" SP nz-number /
"UNSEEN" SP nz-number /
atom [SP 1*<any TEXT-CHAR except "]">]
search = "SEARCH" [SP "CHARSET" SP charset] 1*(SP search-key)
; CHARSET argument to MUST be registered with IANA
search-key = "ALL" / "ANSWERED" / "BCC" SP astring /
"BEFORE" SP date / "BODY" SP astring /
"CC" SP astring / "DELETED" / "FLAGGED" /
"FROM" SP astring / "KEYWORD" SP flag-keyword /
"NEW" / "OLD" / "ON" SP date / "RECENT" / "SEEN" /
"SINCE" SP date / "SUBJECT" SP astring /
"TEXT" SP astring / "TO" SP astring /
"UNANSWERED" / "UNDELETED" / "UNFLAGGED" /
"UNKEYWORD" SP flag-keyword / "UNSEEN" /
; Above this line were in [IMAP2]
"DRAFT" / "HEADER" SP header-fld-name SP astring /
"LARGER" SP number / "NOT" SP search-key /
"OR" SP search-key SP search-key /
"SENTBEFORE" SP date / "SENTON" SP date /
"SENTSINCE" SP date / "SMALLER" SP number /
"UID" SP sequence-set / "UNDRAFT" / sequence-set /
"(" search-key *(SP search-key) ")"
section = "[" [section-spec] "]"
section-msgtext = "HEADER" / "HEADER.FIELDS" [".NOT"] SP header-list /
"TEXT"
; top-level or MESSAGE/RFC822 part
section-part = nz-number *("." nz-number)
; body part nesting
section-spec = section-msgtext / (section-part ["." section-text])
section-text = section-msgtext / "MIME"
; text other than actual body part (headers, etc.)
select = "SELECT" SP mailbox
seq-number = nz-number / "*"
; message sequence number (COPY, FETCH, STORE
; commands) or unique identifier (UID COPY,
; UID FETCH, UID STORE commands).
; * represents the largest number in use. In
; the case of message sequence numbers, it is
; the number of messages in a non-empty mailbox.
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; In the case of unique identifiers, it is the
; unique identifier of the last message in the
; mailbox or, if the mailbox is empty, the
; mailbox's current UIDNEXT value.
; The server should respond with a tagged BAD
; response to a command that uses a message
; sequence number greater than the number of
; messages in the selected mailbox. This
; includes "*" if the selected mailbox is empty.
seq-range = seq-number ":" seq-number
; two seq-number values and all values between
; these two regardless of order.
; Example: 2:4 and 4:2 are equivalent and indicate
; values 2, 3, and 4.
; Example: a unique identifier sequence range of
; 3291:* includes the UID of the last message in
; the mailbox, even if that value is less than 3291.
sequence-set = (seq-number / seq-range) ["," sequence-set]
; set of seq-number values, regardless of order.
; Servers MAY coalesce overlaps and/or execute the
; sequence in any order.
; Example: a message sequence number set of
; 2,4:7,9,12:* for a mailbox with 15 messages is
; equivalent to 2,4,5,6,7,9,12,13,14,15
; Example: a message sequence number set of *:4,5:7
; for a mailbox with 10 messages is equivalent to
; 10,9,8,7,6,5,4,5,6,7 and MAY be reordered and
; overlap coalesced to be 4,5,6,7,8,9,10.
status = "STATUS" SP mailbox SP
"(" status-att *(SP status-att) ")"
status-att = "MESSAGES" / "RECENT" / "UIDNEXT" / "UIDVALIDITY" /
"UNSEEN"
status-att-val = ("MESSAGES" SP number) / ("RECENT" SP number) /
("UIDNEXT" SP nz-number) / ("UIDVALIDITY" SP nz-number) /
("UNSEEN" SP number)
status-att-list = status-att-val *(SP status-att-val)
store = "STORE" SP sequence-set SP store-att-flags
store-att-flags = (["+" / "-"] "FLAGS" [".SILENT"]) SP
(flag-list / (flag *(SP flag)))
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string = quoted / literal
subscribe = "SUBSCRIBE" SP mailbox
tag = 1*<any ASTRING-CHAR except "+">
text = 1*TEXT-CHAR
TEXT-CHAR = <any CHAR except CR and LF>
time = 2DIGIT ":" 2DIGIT ":" 2DIGIT
; Hours minutes seconds
uid = "UID" SP (copy / fetch / search / store)
; Unique identifiers used instead of message
; sequence numbers
uniqueid = nz-number
; Strictly ascending
unsubscribe = "UNSUBSCRIBE" SP mailbox
userid = astring
x-command = "X" atom <experimental command arguments>
zone = ("+" / "-") 4DIGIT
; Signed four-digit value of hhmm representing
; hours and minutes east of Greenwich (that is,
; the amount that the given time differs from
; Universal Time). Subtracting the timezone
; from the given time will give the UT form.
; The Universal Time zone is "+0000".
10. Author's Note
This document is a revision or rewrite of earlier documents, and
supercedes the protocol specification in those documents: RFC 2060,
RFC 1730, unpublished IMAP2bis.TXT document, RFC 1176, and RFC 1064.
11. Security Considerations
IMAP4rev1 protocol transactions, including electronic mail data, are
sent in the clear over the network unless protection from snooping is
negotiated. This can be accomplished either by the use of STARTTLS,
negotiated privacy protection in the AUTHENTICATE command, or some
other protection mechanism.
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11.1. STARTTLS Security Considerations
IMAP client and server implementations MUST implement the
TLS_RSA_WITH_RC4_128_MD5 [TLS] cipher suite, and SHOULD implement the
TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA [TLS] cipher suite. This is
important as it assures that any two compliant implementations can be
configured to interoperate. All other cipher suites are OPTIONAL.
Note that this is a change from section 2.1 of [IMAP-TLS].
During the [TLS] negotiation, the client MUST check its understanding
of the server hostname against the server's identity as presented in
the server Certificate message, in order to prevent man-in-the-middle
attacks. If the match fails, the client SHOULD either ask for
explicit user confirmation, or terminate the connection and indicate
that the server's identity is suspect. Matching is performed
according to these rules:
The client MUST use the server hostname it used to open the
connection as the value to compare against the server name as
expressed in the server certificate. The client MUST NOT use any
form of the server hostname derived from an insecure remote source
(e.g., insecure DNS lookup). CNAME canonicalization is not done.
If a subjectAltName extension of type dNSName is present in the
certificate, it SHOULD be used as the source of the server's
identity.
Matching is case-insensitive.
A "*" wildcard character MAY be used as the left-most name
component in the certificate. For example, *.example.com would
match a.example.com, foo.example.com, etc. but would not match
example.com.
If the certificate contains multiple names (e.g., more than one
dNSName field), then a match with any one of the fields is
considered acceptable.
Both the client and server MUST check the result of the STARTTLS
command and subsequent [TLS] negotiation to see whether acceptable
authentication or privacy was achieved.
11.2. Other Security Considerations
A server error message for an AUTHENTICATE command which fails due to
invalid credentials SHOULD NOT detail why the credentials are
invalid.
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Use of the LOGIN command sends passwords in the clear. This can be
avoided by using the AUTHENTICATE command with a [SASL] mechanism
that does not use plaintext passwords, by first negotiating
encryption via STARTTLS or some other protection mechanism.
A server implementation MUST implement a configuration that, at the
time of authentication, requires:
(1) The STARTTLS command has been negotiated.
OR
(2) Some other mechanism that protects the session from password
snooping has been provided.
OR
(3) The following measures are in place:
(a) The LOGINDISABLED capability is advertised, and [SASL] mechanisms
(such as PLAIN) using plaintext passwords are NOT advertised in the
CAPABILITY list.
AND
(b) The LOGIN command returns an error even if the password is
correct.
AND
(c) The AUTHENTICATE command returns an error with all [SASL]
mechanisms that use plaintext passwords, even if the password is
correct.
A server error message for a failing LOGIN command SHOULD NOT specify
that the user name, as opposed to the password, is invalid.
A server SHOULD have mechanisms in place to limit or delay failed
AUTHENTICATE/LOGIN attempts.
Additional security considerations are discussed in the section
discussing the AUTHENTICATE and LOGIN commands.
12. IANA Considerations
IMAP4 capabilities are registered by publishing a standards track or
IESG approved experimental RFC. The registry is currently located
at: http://www.iana.org/assignments/imap4-capabilities
As this specification revises the STARTTLS and LOGINDISABLED
extensions previously defined in [IMAP-TLS], IANA is requested to
update the registry accordingly.
13. References
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13.1. Normative References
[ABNF] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008,
<http://www.rfc-editor.org/info/rfc5234>.
[ANONYMOUS]
Zeilenga, K., "Anonymous Simple Authentication and
Security Layer (SASL) Mechanism", RFC 4505, June 2006,
<http://www.rfc-editor.org/info/rfc4505>.
[CHARSET] Freed, N. and J. Postel, "IANA Charset Registration
Procedures", BCP 19, RFC 2978, October 2000,
<http://www.rfc-editor.org/info/rfc2978>.
[DIGEST-MD5]
Leach, P. and C. Newman, "Using Digest Authentication as a
SASL Mechanism", RFC 2831, May 2000,
<http://www.rfc-editor.org/info/rfc2831>.
[DISPOSITION]
Troost, R., Dorner, S., and K. Moore, Ed., "Communicating
Presentation Information in Internet Messages: The
Content-Disposition Header Field", RFC 2183, August 1997,
<http://www.rfc-editor.org/info/rfc2183>.
[PLAIN] Zeilenga, K., Ed., "The PLAIN Simple Authentication and
Security Layer (SASL) Mechanism", RFC 4616, August 2006,
<http://www.rfc-editor.org/info/rfc4616>.
[KEYWORDS]
Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[LANGUAGE-TAGS]
Alvestrand, H., "Content Language Headers", RFC 3282, May
2002, <http://www.rfc-editor.org/info/rfc3282>.
[LOCATION]
Palme, J., Hopmann, A., and N. Shelness, "MIME
Encapsulation of Aggregate Documents, such as HTML
(MHTML)", RFC 2557, March 1999,
<http://www.rfc-editor.org/info/rfc2557>.
[MD5] Myers, J. and M. Rose, "The Content-MD5 Header Field",
RFC 1864, October 1995,
<http://www.rfc-editor.org/info/rfc1864>.
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[MIME-HDRS]
Moore, K., "MIME (Multipurpose Internet Mail Extensions)
Part Three: Message Header Extensions for Non-ASCII Text",
RFC 2047, November 1996,
<http://www.rfc-editor.org/info/rfc2047>.
[MIME-IMB]
Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996,
<http://www.rfc-editor.org/info/rfc2045>.
[MIME-IMT]
Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
November 1996, <http://www.rfc-editor.org/info/rfc2046>.
[RFC-5322]
Resnick, P., Ed., "Internet Message Format", RFC 5322,
October 2008, <http://www.rfc-editor.org/info/rfc5322>.
[SASL] Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple
Authentication and Security Layer (SASL)", RFC 4422, June
2006, <http://www.rfc-editor.org/info/rfc4422>.
[TLS] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>.
[UTF-7] Goldsmith, D. and M. Davis, "UTF-7 A Mail-Safe
Transformation Format of Unicode", RFC 2152, May 1997,
<http://www.rfc-editor.org/info/rfc2152>.
[IMAP-IMPLEMENTATION]
Leiba, B., "IMAP4 Implementation Recommendations",
RFC 2683, September 1999,
<http://www.rfc-editor.org/info/rfc2683>.
[IMAP-MULTIACCESS]
Gahrns, M., "IMAP4 Multi-Accessed Mailbox Practice",
RFC 2180, July 1997,
<http://www.rfc-editor.org/info/rfc2180>.
13.2. Informative References (related protocols)
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[IMAP-DISC]
Melnikov, A., Ed., "Synchronization Operations for
Disconnected IMAP4 Clients", RFC 4549, June 2006,
<http://www.rfc-editor.org/info/rfc4549>.
[IMAP-MODEL]
Crispin, M., "Distributed Electronic Mail Models in
IMAP4", RFC 1733, December 1994,
<http://www.rfc-editor.org/info/rfc1733>.
[ACAP] Newman, C. and J. G. Myers, "ACAP -- Application
Configuration Access Protocol", RFC 2244, November 1997,
<http://www.rfc-editor.org/info/rfc2244>.
[SMTP] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
October 2008, <http://www.rfc-editor.org/info/rfc5321>.
13.3. Informative References (historical aspects of IMAP and related
protocols)
[IMAP-COMPAT]
Crispin, M., "IMAP4 Compatibility with IMAP2bis",
RFC 2061, December 1996,
<http://www.rfc-editor.org/info/rfc2061>.
[IMAP-HISTORICAL]
Crispin, M., "IMAP4 Compatibility with IMAP2 and
IMAP2bis", RFC 1732, December 1994,
<http://www.rfc-editor.org/info/rfc1732>.
[IMAP-OBSOLETE]
Crispin, M., "Internet Message Access Protocol - Obsolete
Syntax", RFC 2062, December 1996,
<http://www.rfc-editor.org/info/rfc2062>.
[IMAP2] Crispin, M., "Interactive Mail Access Protocol: Version
2", RFC 1176, August 1990,
<http://www.rfc-editor.org/info/rfc1176>.
[RFC-822] Crocker, D., "STANDARD FOR THE FORMAT OF ARPA INTERNET
TEXT MESSAGES", STD 11, RFC 822, August 1982,
<http://www.rfc-editor.org/info/rfc822>.
[RFC-821] Postel, J., "Simple Mail Transfer Protocol", STD 10,
RFC 821, August 1982,
<http://www.rfc-editor.org/info/rfc821>.
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[IMAP-TLS]
Newman, C., "Using TLS with IMAP, POP3 and ACAP",
RFC 2595, June 1999,
<http://www.rfc-editor.org/info/rfc2595>.
Appendix A. Changes from RFC 3501
1. Updated references.
2. Applied errata: 261, 3032, 3093
Appendix B. Acknowledgement
Earlier versions of this document were edited by Mark Crispin.
Sadly, he is no longer available to help with this work. Editor of
this revisions is hoping that Mark would have approved.
Thank you to Tony Hansen for helping with the index generation.
Index
+
+FLAGS <flag list> 54
+FLAGS.SILENT <flag list> 54
-
-FLAGS <flag list> 55
-FLAGS.SILENT <flag list> 55
A
ALERT (response code) 59
ALL (fetch item) 51
ALL (search key) 48
ANSWERED (search key) 48
APPEND (command) 43
AUTHENTICATE (command) 27
B
BAD (response) 61
BADCHARSET (response code) 59
BCC <string> (search key) 48
BEFORE <date> (search key) 48
BODY (fetch item) 51
BODY (fetch result) 68
BODY <string> (search key) 48
BODY.PEEK[<section>]<<partial>> (fetch item) 53
BODYSTRUCTURE (fetch item) 53
BODYSTRUCTURE (fetch result) 68
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BODY[<section>]<<origin octet>> (fetch result) 68
BODY[<section>]<<partial>> (fetch item) 51
BYE (response) 62
Body Structure (message attribute) 13
C
CAPABILITY (command) 23
CAPABILITY (response code) 59
CAPABILITY (response) 63
CC <string> (search key) 48
CHECK (command) 45
CLOSE (command) 45
COPY (command) 55
CREATE (command) 33
D
DELETE (command) 34
DELETED (search key) 48
DRAFT (search key) 48
E
ENVELOPE (fetch item) 53
ENVELOPE (fetch result) 71
EXAMINE (command) 32
EXPUNGE (command) 46
EXPUNGE (response) 67
Envelope Structure (message attribute) 12
F
FAST (fetch item) 51
FETCH (command) 50
FETCH (response) 68
FLAGGED (search key) 48
FLAGS (fetch item) 53
FLAGS (fetch result) 72
FLAGS (response) 65
FLAGS <flag list> (store command data item) 54
FLAGS.SILENT <flag list> (store command data item) 54
FROM <string> (search key) 48
FULL (fetch item) 51
Flags (message attribute) 11
H
HEADER (part specifier) 51
HEADER <field-name> <string> (search key) 48
HEADER.FIELDS (part specifier) 51
HEADER.FIELDS.NOT (part specifier) 51
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I
INTERNALDATE (fetch item) 53
INTERNALDATE (fetch result) 72
Internal Date (message attribute) 12
K
KEYWORD <flag> (search key) 48
Keyword (type of flag) 12
L
LARGER <n> (search key) 48
LIST (command) 38
LIST (response) 64
LOGOUT (command) 25
LSUB (command) 41
LSUB (response) 65
M
MAY (specification requirement term) 5
MESSAGES (status item) 43
MIME (part specifier) 52
MUST (specification requirement term) 5
MUST NOT (specification requirement term) 5
Message Sequence Number (message attribute) 10
N
NEW (search key) 48
NO (response) 61
NOOP (command) 24
NOT <search-key> (search key) 48
O
OK (response) 60
OLD (search key) 48
ON <date> (search key) 49
OPTIONAL (specification requirement term) 5
OR <search-key1> <search-key2> (search key) 49
P
PARSE (response code) 59
PERMANENTFLAGS (response code) 59
PREAUTH (response) 61
Permanent Flag (class of flag) 12
R
READ-ONLY (response code) 60
READ-WRITE (response code) 60
RECENT (search key) 49
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RECENT (status item) 43
RECOMMENDED (specification requirement term) 5
RENAME (command) 35
REQUIRED (specification requirement term) 5
RFC822 (fetch item) 53
RFC822 (fetch result) 72
RFC822.HEADER (fetch item) 53
RFC822.HEADER (fetch result) 72
RFC822.SIZE (fetch item) 53
RFC822.SIZE (fetch result) 72
RFC822.TEXT (fetch item) 53
RFC822.TEXT (fetch result) 72
S
SEARCH (command) 47
SEARCH (response) 65
SEEN (search key) 49
SELECT (command) 30
SENTBEFORE <date> (search key) 49
SENTON <date> (search key) 49
SENTSINCE <date> (search key) 49
SHOULD (specification requirement term) 5
SHOULD NOT (specification requirement term) 5
SINCE <date> (search key) 49
SMALLER <n> (search key) 49
STARTTLS (command) 26
STATUS (command) 42
STATUS (response) 65
STORE (command) 54
SUBJECT <string> (search key) 49
SUBSCRIBE (command) 37
Session Flag (class of flag) 12
System Flag (type of flag) 11
T
TEXT (part specifier) 51
TEXT <string> (search key) 49
TO <string> (search key) 49
TRYCREATE (response code) 60
U
UID (command) 56
UID (fetch item) 53
UID (fetch result) 72
UID <sequence set> (search key) 49
UIDNEXT (response code) 60
UIDNEXT (status item) 43
UIDVALIDITY (response code) 60
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UIDVALIDITY (status item) 43
UNANSWERED (search key) 49
UNDELETED (search key) 49
UNDRAFT (search key) 49
UNFLAGGED (search key) 49
UNKEYWORD <flag> (search key) 50
UNSEEN (response code) 60
UNSEEN (search key) 50
UNSEEN (status item) 43
UNSUBSCRIBE (command) 38
Unique Identifier (UID) (message attribute) 9
X
X<atom> (command) 57
[
[RFC-5322] Size (message attribute) 12
\
\Answered (system flag) 11
\Deleted (system flag) 11
\Draft (system flag) 11
\Flagged (system flag) 11
\Marked (mailbox name attribute) 64
\Noinferiors (mailbox name attribute) 64
\Noselect (mailbox name attribute) 64
\Recent (system flag) 11
\Seen (system flag) 11
\Unmarked (mailbox name attribute) 64
Author's Address
Alexey Melnikov (editor)
Isode Ltd
14 Castle Mews
Hampton, Middlesex TW12 2NP
UK
Email: Alexey.Melnikov@isode.com
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