Internet DRAFT - draft-duerst-eai-mailto
draft-duerst-eai-mailto
Network Working Group M. Duerst
Internet-Draft Aoyama Gakuin University
Obsoletes: 6068 (if approved) L. Masinter
Intended status: Standards Track Adobe Systems Incorporated
Expires: March 29, 2013 J. Zawinski
DNA Lounge
September 25, 2012
The 'mailto' URI/IRI Scheme
draft-duerst-eai-mailto-04
Abstract
This document defines the format of Uniform Resource Identifiers
(URIs) and Internationalized Resource Identfiers (IRIs) to identify
resources that are reached using Internet mail. It adds the
possibility to use Email Address Internationalization (EAI) email
addresses (RFC6530) to the previous syntax of 'mailto' URIs (RFC
6068).
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."
This Internet-Draft will expire on March 29, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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to this document. Code Components extracted from this document must
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This document may contain material from IETF Documents or IETF
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Syntax of a 'mailto' URI . . . . . . . . . . . . . . . . . . . 4
2.1. Syntax Rules . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Additional Details about <addr-spec-enc> . . . . . . . . . 5
2.3. Additional Details about <hfname> and <hfvalue> . . . . . 6
3. Semantics and Operations . . . . . . . . . . . . . . . . . . . 8
4. Unsafe Header Fields . . . . . . . . . . . . . . . . . . . . . 9
5. Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6.1. Conventions Used . . . . . . . . . . . . . . . . . . . . . 11
6.2. Basic Examples . . . . . . . . . . . . . . . . . . . . . . 11
6.3. Examples of Complicated Email Addresses . . . . . . . . . 12
6.4. Examples Using UTF-8-Based Percent-Encoding usable
with RFC 5322 . . . . . . . . . . . . . . . . . . . . . . 13
6.5. Examples Using UTF-8-Based Percent-Encoding usable
only with EAI . . . . . . . . . . . . . . . . . . . . . . 15
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
8.1. Update of the Registration of the 'mailto' URI/IRI
Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8.2. Registration of the Body Header Field . . . . . . . . . . 19
9. Main Changes from RFC 6068 . . . . . . . . . . . . . . . . . . 19
10. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 19
10.1. Changes from -03 to -04 . . . . . . . . . . . . . . . . . 19
10.2. Changes from -02 to -03 . . . . . . . . . . . . . . . . . 20
10.3. Changes from -01 to -02 . . . . . . . . . . . . . . . . . 20
10.4. Changes from -00 to -01 . . . . . . . . . . . . . . . . . 20
10.5. Changes from RFC 6068 to -00 . . . . . . . . . . . . . . . 20
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
12.1. Normative References . . . . . . . . . . . . . . . . . . . 21
12.2. Informative References . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
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1. Introduction
The 'mailto' URI/IRI scheme is a URI/IRI scheme [RFC4395bis] used to
identify resources that are reached using Internet mail. In its
simplest form, a 'mailto' URI/IRI contains an Internet mail address.
For interactions that require message headers or message bodies to be
specified, the 'mailto' URI/IRI scheme also allows providing mail
header fields and a message body.
This specification extends the previous scheme definition ([RFC6068])
to also allow non-ASCII characters in the left-hand sides (LHSs) of
email addresses. To work seamlessly with Internationalized Resource
Identfiers (IRIs, [RFC3987]) and Email Address Internationalization
(EAI, [RFC6530]), these LHSs are percent-encoded based on UTF-8
[STD63] when used in URIs.
This document is available in (line-printer ready) plaintext ASCII
and PDF. It is also available in HTML from http://
www.sw.it.aoyama.ac.jp/2012/pub/draft-duerst-eai-mailto-04.html, and
in UTF-8 plaintext from http://www.sw.it.aoyama.ac.jp/2012/pub/
draft-ietf-duerst-eai-mailto-04.utf8.txt. While all these versions
are identical in their technical content, the HTML, PDF, and UTF-8
plaintext versions show non-Unicode characters directly. This often
makes it easier to understand examples, and readers are therefore
advised to consult these versions in preference or as a supplement to
the ASCII version.
Example URIs and IRIs are enclosed in '<' and '>' as described in
Appendix C of [STD66]. Extra whitespace and line breaks are added to
present long URIs -- they are not part of the actual URI.
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 [RFC2119].
2. Syntax of a 'mailto' URI
2.1. Syntax Rules
The syntax of a 'mailto' URI is described using the ABNF of [STD68].
The syntax of a 'mailto' IRI can be obtained from this definition by
allowing <iunreserved> characters wherever <unreserved> characters
are allowed. The syntax below also uses non-terminal definitions
from [STD66] (unreserved, pct-encoded):
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mailtoURI = "mailto:" [ to ] [ hfields ]
to = addr-spec-enc *("," addr-spec-enc )
hfields = "?" hfield *( "&" hfield )
hfield = hfname "=" hfvalue
hfname = *qchar
hfvalue = *qchar
addr-spec-enc = local-part-enc "@" domain-enc
local-part-enc = dot-atom-text-enc / quoted-string-enc
domain-enc = dot-atom-text-enc / "[" *dtext-no-obs "]"
dtext-no-obs = %d33-90 ; Printable US-ASCII
/ %d94-126 ; characters not including
; "[", "]", or "\"
dot-atom-text-enc = <percent-encoded version of
dot-atom-text or its EAI equivalent>
quoted-string-enc = <percent-encoded version of
dot-atom-text or its EAI equivalent>
qchar = unreserved / pct-encoded / some-delims
some-delims = "!" / "$" / "'" / "(" / ")" / "*"
/ "+" / "," / ";" / ":" / "@" / "/" / "?"
In addition to the above syntax rules, the details given in the next
two subsections are relevant.
2.2. Additional Details about <addr-spec-enc>
<addr-spec-enc> is a mail address as specified by <addr-spec> in
[RFC5322] or <uAddr-Spec> in [RFC6532], but excluding <comment>, with
the following changes:
1. A number of characters that can appear in <addr-spec> MUST be
percent-encoded. These are the characters that cannot appear in
a URI according to [STD66] as well as "%" (because it is used for
percent-encoding) and all the characters in gen-delims except "@"
and ":" (i.e., "/", "?", "#", "[", and "]"). Of the characters
in sub-delims, at least the following also have to be percent-
encoded: "&", ";", and "=". Care has to be taken both when
encoding as well as when decoding to make sure these operations
are applied only once.
2. <obs-local-part> and <NO-WS-CTL> as defined in [RFC5322] MUST NOT
be used.
3. Whitespace and comments within <local-part-enc> and <domain-enc>
MUST NOT be used. They would not have any operational semantics.
4. Percent-encoding can be used in the <domain-enc> part of an
<addr-spec-enc>, in order to denote an internationalized domain
name. The considerations for <reg-name> in [STD66] apply. In
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particular, non-ASCII characters MUST first be encoded according
to UTF-8 [STD63], and then each octet of the corresponding UTF-8
sequence MUST be percent-encoded to be represented as URI
characters. URI-producing applications MUST NOT use percent-
encoding in domain names unless it is used to represent a UTF-8
character sequence. When the internationalized domain name is
used to compose a message, the name MUST be transformed to the
Internationalizing Domain Names in Applications (IDNA) encoding
[RFC5891] where appropriate. URI producers SHOULD provide these
domain names in the IDNA encoding, rather than percent-encoded,
if they wish to maximize interoperability with legacy 'mailto'
URI interpreters.
5. Percent-encoding of non-ASCII octets in the <local-part-enc> of
an <addr-spec-enc> is used for the internationalization of the
<local-part-enc> according to Email Address Internationalization
(EAI; [RFC6532]). Non-ASCII characters MUST first be encoded
according to UTF-8 [STD63], and then each octet of the
corresponding UTF-8 sequence MUST be percent-encoded to be
represented as URI characters. Any other percent-encoding of
non-ASCII characters is prohibited. When a <local-part-enc>
containing non-ASCII characters will be used to compose a
message, the <local-part-enc> MUST be transformed back to UTF-8
in order to conform to EAI.
<dot-atom-text-enc> is the percent-encoded version of <dot-atom-text>
in [RFC5322] or <uDot-Atom-text> in [RFC6532]. <quoted-string-enc> is
the percent-encoded version of <quoted-string> in [RFC5322] or
<uQuoted-String> in [RFC6532].
2.3. Additional Details about <hfname> and <hfvalue>
<hfname> and <hfvalue> are encodings of an [RFC5322] header field
name and value, respectively. Percent-encoding is needed for the
same characters as listed above for <addr-spec-enc>. <hfname> is
case-insensitive, but <hfvalue> in general is case-sensitive. Note
that [RFC5322] allows all US-ASCII printable characters except ":" in
optional header field names (Section 3.6.8), which is the reason why
<pct-encoded> is part of the header field name production.
The special <hfname> "body" indicates that the associated <hfvalue>
is the body of the message. The "body" field value is intended to
contain the content for the first text/plain body part of the
message. The "body" pseudo header field is primarily intended for
the generation of short text messages for automatic processing (such
as "subscribe" messages for mailing lists), not for general MIME
bodies. Except for the encoding of characters based on UTF-8 and
percent-encoding, no additional encoding (such as e.g., base64 or
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quoted-printable; see [RFC2045]) is used for the "body" field value.
As a consequence, header fields related to message encoding (e.g.,
Content-Transfer-Encoding) in a 'mailto' URI are irrelevant and MUST
be ignored. The "body" pseudo header field name has been registered
with IANA for this special purpose (see Section 8.2).
Within 'mailto' URIs, the characters "?", "=", and "&" are reserved,
serving as delimiters. They have to be escaped (as "%3F", "%3D", and
"%26", respectively) when not serving as delimiters.
Additional restrictions on what characters are allowed might apply
depending on the context where the URI is used. Such restrictions
can be addressed by context-specific escaping mechanisms. For
example, because the "&" (ampersand) character is reserved in HTML
and XML, any 'mailto' URI that contains an ampersand has to be
written with an HTML/XML entity ("&") or numeric character
reference ("&" or "&").
Non-ASCII characters can be encoded in <hfvalue> as follows:
1. MIME encoded words (as defined in [RFC2047]) are permitted in
header field values, but not in an <hfvalue> of a "body"
<hfname>. Sequences of characters that look like MIME encoded
words can appear in an <hfvalue> of a "body" <hfname>, but in
that case have no special meaning. Please note that the '=' and
'?' characters used as delimiters in MIME encoded words have to
be percent-encoded. Also note that the use of MIME encoded words
differs slightly for so-called structured and unstructured header
fields.
2. Non-ASCII characters MUST be encoded according to UTF-8 [STD63] ,
and then each octet of the corresponding UTF-8 sequence is
percent-encoded to be represented as URI characters. When header
field values encoded in this way are used to compose a message
conforming to [RFC5322], the <hfvalue> has to be suitably encoded
(transformed into MIME encoded words [RFC2047]), except for an
<hfvalue> of a "body" <hfname>, which has to be encoded according
to [RFC2045]. Please note that for MIME encoded words and for
bodies in composed email messages, encodings other than UTF-8 MAY
be used as long as the characters are properly transcoded. When
header field values encoded in this way are used to compose a
message conforming to [RFC6532], percent-encoding (including
reserved characters) has to be decoded. The header field values
can then be used directly because EAI allows UTF-8 in header
field values.
Note that it is syntactically valid to specify both <to> and an
<hfname> whose value is "to". That is,
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<mailto:addr1@an.example,addr2@an.example>
is equivalent to
<mailto:?to=addr1@an.example,addr2@an.example>
is equivalent to
<mailto:addr1@an.example?to=addr2@an.example>
However, the latter two forms are NOT RECOMMENDED because different
user agents handle this case differently. In particular, some
existing clients ignore "to" <hfvalue>s.
Implementations MUST NOT produce two "To:" header fields in a
message; the "To:" header field may occur at most once in a message
([RFC5322], Section 3.6). Also, creators of 'mailto' URIs MUST NOT
include other message header fields multiple times if these header
fields can only be used once in a message.
To avoid interoperability problems, creators of 'mailto' URIs SHOULD
NOT use the same <hfname> multiple times in the same URI. If the
same <hfname> appears multiple times in a URI, behavior varies widely
for different user agents, and for each <hfname>. Examples include
using only the first or last <hfname>/<hfvalue> pair, creating
multiple header fields, and combining each <hfvalue> by simple
concatenation or in a way appropriate for the corresponding header
field.
Note that this specification, like any URI/IRI scheme specification,
does not define syntax or meaning of a fragment identifier (see
[STD66]), because these depend on the type of a retrieved
representation. In the currently known usage scenarios, a 'mailto'
URI cannot be used to retrieve such representations. The character
"#" in <hfvalue>s MUST be escaped as %23.
3. Semantics and Operations
A 'mailto' URI/IRI designates an "Internet resource", which is the
mailbox specified in the address. When additional header fields are
supplied, the resource designated is the same address but with an
additional profile for accessing the resource. While there are
Internet resources that can only be accessed via electronic mail, the
'mailto' URI is not intended as a way of retrieving such objects
automatically.
The operation of how any URI/IRI scheme is resolved is not mandated
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by the URI specifications. In current practice, resolving URIs/IRIs
such as those in the 'http' URI/IRI scheme causes an immediate
interaction between client software and a host running an interactive
server. The 'mailto' URI/IRI has unusual semantics because resolving
such a URI/IRI does not necessarily cause an immediate interaction
with a server. Instead, the client creates a message to the
designated address with the various header fields set as default.
The user can edit the message, send the message unedited, or choose
not to send the message.
Note that with the introduction of the possibility to register
handlers of URI/IRI schemes to web applications, there is no longer a
guarantee that the resolution of a 'mailto' URI/IRI is purely local.
Registering a web mail service as a handler of 'mailto' URIs/IRIs
means that the creation of a message to the designated address is
done with the help and knowledge of that web mail service.
The <hfname>/<hfvalue> pairs in a 'mailto' URI/IRI, although
syntactically equivalent to header fields in a mail message, do not
directly correspond to the header fields in a mail message. In
particular, the To, Cc, and Bcc <hfvalue>s don't necessarily result
in a header field containing the specified value. Mail client
software MAY eliminate duplicate addresses. Creators of 'mailto'
URIs SHOULD avoid using the same address twice in a 'mailto' URI/IRI.
Originator fields like From and Date, fields related to routing
(Apparently-To, Resent-*, etc.), trace fields, and MIME header fields
(MIME-Version, Content-*), when present in the URI/IRI, MUST be
ignored. The mail client MUST create new fields when necessary, as
it would for any new message. Unrecognized header fields and header
fields with values inconsistent with those the mail client would
normally send SHOULD be treated as especially suspect. For example,
there may be header fields that are totally safe but not known to the
MUA, so the MUA MAY choose to show them to the user.
4. Unsafe Header Fields
The user agent interpreting a 'mailto' URI/IRI SHOULD NOT create a
message if any of the header fields are considered dangerous; it MAY
also choose to create a message with only a subset of the header
fields given in the URI/IRI. Only a limited set of header fields
such as Subject and Keywords, as well as Body, are believed to be
both safe and useful in the general case. In cases where the source
of a URI/IRI is well known, and/or specific header fields are limited
to specific well-known values, other header fields MAY be considered
safe, too.
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The creator of a 'mailto' URI/IRI cannot expect the resolver of a
URI/IRI to understand more than the "subject" header field and
"body". Clients that resolve 'mailto' URIs/IRIs into mail messages
MUST be able to correctly create [RFC5322]-compliant mail messages
using the "subject" header field and "body".
5. Encoding
[STD66] requires that many characters in URIs/IRIs be encoded. This
affects the 'mailto' URI/IRI scheme for some common characters that
might appear in addresses, header fields, or message contents. One
such character is space (" ", ASCII hex 20). Note the examples below
that use "%20" for space in the message body. Also note that line
breaks in the body of a message MUST be encoded with "%0D%0A".
Implementations MAY add a final line break to the body of a message
even if there is no trailing "%0D%0A" in the body <hfield> of the
'mailto' URI/IRI. Line breaks in other <hfield>s SHOULD NOT be used.
When creating 'mailto' URIs/IRIs, any reserved characters that are
used in the URIs/IRIs MUST be encoded so that properly written URI/
IRI interpreters can read them. Also, client software that reads
URIs/IRIs MUST decode strings before creating the mail message so
that the mail message appears in a form that the recipient software
will understand. These strings SHOULD be decoded before showing the
message to the sending user.
Software creating 'mailto' URIs/IRIs likewise has to be careful to
encode any reserved characters that are used. HTML forms are one
kind of software that creates 'mailto' URIs/IRIs. Current
implementations encode a space as '+', but this creates problems
because such a '+' standing for a space cannot be distinguished from
a real '+' in a 'mailto' URI/IRI. When producing 'mailto' URIs/IRIs,
all spaces SHOULD be encoded as %20, and '+' characters MAY be
encoded as %2B. Please note that '+' characters are frequently used
as part of an email address to indicate a subaddress, as for example
in <bill+ietf@example.org>.
The 'mailto' URI/IRI scheme is limited in that it does not provide
for substitution of variables. Thus, it is impossible to create a
'mailto' URI/IRI that includes a user's email address in the message
body. This limitation also prevents 'mailto' URIs/IRIs that are
signed with public keys and other such variable information.
6. Examples
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6.1. Conventions Used
To represent characters outside US-ASCII in a document format that is
limited to US-ASCII, this document uses 'XML Notation'. A non-ASCII
character is denoted by a leading '&#x', a trailing ';', and the
hexadecimal number of the character in the UCS in between. For
example, Я stands for CYRILLIC CAPITAL LETTER YA. An actual
'&' is denoted by '&'. This notation is only used in the ASCII
version(s) of this document, because in the other versions, non-ASCII
characters are used directly.
Where the IRI form of an example is identical to the URI form, only
one form is given. If the IRI form is different, then both forms are
given.
6.2. Basic Examples
A URI for an ordinary individual mailing address:
<mailto:chris@example.com>
A URI for a mail response system that requires the name of the file
to be sent back in the subject:
<mailto:infobot@example.com?subject=current-issue>
A mail response system that requires a "send" request in the body:
<mailto:infobot@example.com?body=send%20current-issue>
A similar URI, with two lines with different "send" requests (in this
case, "send current-issue" and, on the next line, "send index"):
<mailto:infobot@
example.com?body=send%20current-issue%0D%0Asend%20index>
An interesting use of 'mailto' URIs occurs when browsing archives of
messages. A link can be provided that allows replying to a message
and conserving threading information. This is done by adding an In-
Reply-To header field containing the Message-ID of the message where
the link is added, for example:
<mailto:list@example.org?In-Reply-To=%3C3469A91.D10AF4C@
example.com%3E>
A request to subscribe to a mailing list:
<mailto:majordomo@example.com?body=subscribe%20bamboo-l>
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A URI that is for a single user and that includes a CC of another
user:
<mailto:joe@example.com?cc=bob@example.com&body=hello>
Note the use of the "&" reserved character above. The following
example, using "?" twice, is incorrect:
<mailto:joe@example.com?cc=bob@example.com?body=hello> ; WRONG!
According to [RFC5322], the characters "?", "&", and even "%" may
occur in <addr-spec>s. The fact that they are reserved characters is
not a problem: those characters may appear in 'mailto' URIs -- they
just may not appear in unencoded form. The standard URI encoding
mechanisms ("%" followed by a two-digit hex number) MUST be used in
these cases.
To indicate the address "gorby%kremvax@example.com" one would use:
<mailto:gorby%25kremvax@example.com>
To indicate the address "unlikely?address@example.com", and include
another header field, one would use:
<mailto:unlikely%3Faddress@example.com?blat=foop>
As described above, the "&" (ampersand) character is reserved in HTML
and has to be replaced, e.g., with "&". Thus, in an HTML context
a URI with an internal ampersand might look like:
Click <a
href="mailto:joe@an.example?cc=bob@an.example&body=hello"
>mailto:joe@an.example?cc=bob@an.example&body=hello</a>
to send a greeting message to Joe and Bob.
When an email address itself includes an "&" (ampersand) character,
that character has to be percent-encoded. For example, the 'mailto'
URI to send mail to "Mike&family@example.org" is
<mailto:Mike%26family@example.org>.
6.3. Examples of Complicated Email Addresses
Following are a few examples of how to treat email addresses that
contain complicated escaping syntax.
Email address: not@me"@example.org; corresponding 'mailto' URI:
<mailto:%22not%40me%22@example.org>.
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Email address: "oh\\no"@example.org; corresponding 'mailto' URI:
<mailto:%22oh%5C%5Cno%22@example.org>.
Email address: "\\\"it's\ ugly\\\""@example.org; corresponding
'mailto' URI:
<mailto:%22%5C%5C%5C%22it's%5C%20ugly%5C%5C%5C%22%22@example.org>.
6.4. Examples Using UTF-8-Based Percent-Encoding usable with RFC 5322
Sending a mail with the subject "coffee" in French, i.e., "cafe"
where the final e is an e-acute, using UTF-8 and percent-encoding, as
an URI:
<mailto:user@example.org?subject=caf%C3%A9>
The same as an IRI:
<mailto:user@example.org?subject=café>
The same subject, this time using an encoded-word (escaping the "="
and "?" characters used in the encoded-word syntax, because they are
reserved):
<mailto:user@
example.org?subject=%3D%3Futf-8%3FQ%3Fcaf%3DC3%3DA9%3F%3D>
The same subject, this time encoded as iso-8859-1:
<mailto:user@
example.org?subject=%3D%3Fiso-8859-1%3FQ%3Fcaf%3DE9%3F%3D>
Going back to straight UTF-8 and adding a body with the same value,
as an URI:
<mailto:user@example.org?subject=caf%C3%A9&body=caf%C3%A9>
The same as an IRI:
<mailto:user@example.org?subject=café&body=café>
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This 'mailto' URI may result in an [RFC5322] message looking like
this:
From: sender@example.net
To: user@example.org
Subject: =?utf-8?Q?caf=C3=A9?=
Content-Type: text/plain;charset=utf-8
Content-Transfer-Encoding: quoted-printable
caf=C3=A9
The software sending the email is not restricted to UTF-8, but can
use other encodings. The following shows the same email using iso-
8859-1 two times:
From: sender@example.net
To: user@example.org
Subject: =?iso-8859-1?Q?caf=E9?=
Content-Type: text/plain;charset=iso-8859-1
Content-Transfer-Encoding: quoted-printable
caf=E9
Different content transfer encodings (i.e., "8bit" or "base64"
instead of "quoted-printable") and different encodings in encoded
words (i.e., "B" instead of "Q") can also be used.
In a context where EAI is supported, this 'mailto' URI can result in
an [RFC6532] message looking like this (encoded as UTF-8 on the
wire):
From: sender@example.net
To: user@example.org
Subject: café
Content-Type: text/plain;charset=utf-8
Content-Transfer-Encoding: 8bit
café
For more examples of encoding the word coffee in different languages,
see [RFC2324].
The following example uses the Japanese word "natto" (Unicode
characters U+7D0D U+8C46) as a domain name label, sending a mail to a
user at 納豆.example.org, as an URI:
<mailto:user@%E7%B4%8D%E8%B1%86.example.org?subject=Test&
body=%E7%B4%8D%E8%B1%86>
The same as an IRI:
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<mailto:user@納豆.example.org?subject=Test&
body=納豆>
When constructing the email for use with [RFC5322], the domain name
label is converted to punycode. The resulting message might look as
follows:
From: sender@example.net
To: user@xn--99zt52a.example.org
Subject: Test
Content-Type: text/plain;charset=utf-8
Content-Transfer-Encoding: base64
57SN6LGG
The same message using EAI ([RFC6532]) can look as follows (encoded
as UTF-8 on the wire):
From: sender@example.net
To: user@納豆.example.org
Subject: Test
Content-Type: text/plain;charset=utf-8
Content-Transfer-Encoding: 8bit
納豆
6.5. Examples Using UTF-8-Based Percent-Encoding usable only with EAI
All the previous 'mailto' URIs can be used with EAI. When used with
EAI, there is no need to use punycode in domain names, and no need to
use MIME encoding in headers and bodies. After decoding percent-
encoding, UTF-8 can be used directly. This subsection gives a few
additional examples of 'mailto' URI and IRIs which can only be used
with EAI.
Please note that the choice of URI vs. IRI is independent of whether
EAI can be used or not.
A hypothetical 'mailto' URI for ordering coffee from a French coffee
pot:
mailto:caf%C3%A9@pot.example?Subject=Espresso,%20please
The same as an IRI:
mailto:café@pot.example?Subject=Espresso,%20please
A hypothetical 'mailto' URI for sending a potential erratum to the
first author of this memo ("%C3%BC" represents an u-umlaut, "%E9%9D%
92%E5%B1%B1" represents the Unicode characters U+9752 (blue) and
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U+5C71 (mountain)):
mailto:Martin.D%C3%BCrst@%E9%9D%92%E5%B1%
B1.example.net?Subject=Error%20in%20RFC6068bis
The same as an IRI:
mailto:Martin.Dürst@青&#
x5C71;.example.net?Subject=Error%20in%20RFC6068bis
7. Security Considerations
The 'mailto' URI/IRI scheme can be used to send a message from one
user to another, and thus can introduce many security concerns. Mail
messages can be logged at the originating site, the recipient site,
and intermediary sites along the delivery path. If the messages are
not encrypted, they can also be read at any of those sites.
Also, if a web mail service is registered as a handler of 'mailto'
URIs/IRIs, this means that the creation of a message to the
designated address is done with the knowledge of that web mail
service, even if the message is actually never sent.
A 'mailto' URI/IRI gives a template for a message that can be sent by
mail client software. The contents of that template may be opaque or
difficult to read by the user at the time of specifying the URI/IRI,
as well as being hidden in the user interface (for example, a link on
an HTML Web page might display something other than the content of
the corresponding 'mailto' URI/IRI that would be used when clicked).
Thus, a mail client SHOULD NOT send a message based on a 'mailto'
URI/IRI without first disclosing and showing to the user the full
message that will be sent (including all header fields that were
specified by the 'mailto' URI/IRI), fully decoded, and asking the
user for approval to send the message as electronic mail. The mail
client SHOULD also make it clear that the user is about to send an
electronic mail message, since the user may not be aware that this is
the result of a 'mailto' URI/IRI. Users are strongly encouraged to
ensure that the 'mailto' URI/IRI presented to them matches the
address included in the "To:" line of the email message.
Some header fields are inherently unsafe to include in a message
generated from a URI/IRI. For details, please see Section 3. In
general, the fewer header fields interpreted from the URI/IRI, the
less likely it is that a sending agent will create an unsafe message.
Examples of problems with sending unapproved mail include:
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mail that breaks laws upon delivery, such as making illegal
threats;
mail that identifies the sender as someone interested in breaking
laws;
mail that identifies the sender to an unwanted third party;
mail that causes a financial charge to be incurred by the sender;
mail that causes an action on the recipient machine that causes
damage that might be attributed to the sender.
Programs that interpret 'mailto' URIs/IRIs SHOULD ensure that the
SMTP envelope return path address, which is given as an argument to
the SMTP MAIL FROM command, is set and correct, and that the
resulting email is a complete, workable message.
'mailto' URIs/IRIs on public Web pages expose mail addresses for
harvesting. This applies to all mail addresses that are part of the
'mailto' URI/IRI, including the addresses in a "bcc" <hfvalue>.
Those addresses will not be sent to the recipients in the 'to' field
and in the "to" and "cc" <hfvalue>s, but will still be publicly
visible in the URI/IRI. Addresses in a "bcc" <hfvalue> may also leak
to other addresses in the same <hfvalue> or become known otherwise,
depending on the mail user agent used.
Programs manipulating 'mailto' URIs/IRIs have to take great care to
not inadvertently double-escape or double-unescape 'mailto' URIs/
IRIs, and to make sure that escaping and unescaping conventions
relating to URIs/IRIs and relating to mail addresses are applied in
the right order.
Implementations parsing 'mailto' URIs/IRIs must take care to sanity
check 'mailto' URIs/IRIs in order to avoid buffer overflows and
problems resulting from them (e.g., execution of code specified by
the attacker).
The security considerations for URIs ([STD66]), IRIs ([RFC3987]),
IDNA ([RFC5890] and [RFC5891]), and EAI ([RFC6530] and [RFC6532])
also apply. Implementers and users are advised to check them
carefully.
8. IANA Considerations
8.1. Update of the Registration of the 'mailto' URI/IRI Scheme
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This document changes the definition of the 'mailto' URI/IRI scheme;
the registry of URI/IRI schemes should be updated to refer to this
document rather than its predecessor [RFC6068]. The registration
template is as follows:
Resource Identifier (RI) Scheme name:
'mailto'
Status:
permanent
Scheme syntax:
See the syntax section of RFC YYYY.
[RFC Editor: Please replace with actual RFC number.]
Scheme semantics:
See the semantics section of RFC YYYY.
[RFC Editor: Please replace with actual RFC number.]
Encoding considerations:
See the syntax and encoding sections of RFC YYYY.
[RFC Editor: Please replace with actual RFC number.]
Applications/protocols that use this scheme name:
The 'mailto' URI/IRI scheme is widely used since
the start of the Web.
Interoperability considerations:
Interoperability for 'mailto' URIs/IRIs with UTF-8-based
percent-encoding might be somewhat lower than interoperability
for 'mailto' URIs with US-ASCII only. In particular,
interoperability for 'mailto' URIs/IRIs with UTF-8-based
percent-encoding in the LHS of email addresses requires
support of EAI [RFC6530].
Security considerations:
See the security considerations section of RFC YYYY.
[RFC Editor: Please replace with actual RFC number.]
Contact:
IETF
Author/Change controller:
IETF
References:
Duerst, M., Masinter, L., and J. Zawinski,
"The 'mailto' URI/IRI Scheme", RFC YYYY, ???? 201?.
[RFC Editor: Please replace with actual RFC number and date.]
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8.2. Registration of the Body Header Field
IANA is herewith requested to update the reference for the
registration of the Body header field in the Message Header Fields
Registry ([RFC3864]) from [RFC6068] to this document (there are no
changes to the specification of the Body header field itself).
9. Main Changes from RFC 6068
The main changes from [RFC6068] are as follows:
o Allowed UTF-8/percent-encoding in <local-part-enc>, to be used for
EAI email addresses.
o Added "/" and "?" back to some-delims, because they are allowed in
query parts.
o Added suffix "-enc" to some ABNF rule names to distinguish them
from their counterparts without percent-encoding.
o Added a MUST for using UTF-8 in <hfvalue>.
o Added examples as IRIs where there's a difference to the URI form.
o Added non-ASCII examples in HTML and PDF versions for better
understanding.
10. Change Log
RFC Editor: Please remove this section before publication.
10.1. Changes from -03 to -04
Added explanation of consequences of registration of URI/IRI to
web mail service, both in Semantics section and in Security
Considerations.
Alligned registration template with the one in
draft-ietf-iri-4395bis-irireg-04.
Added EAI references and acronyms to security section.
Removed sentence "Therefore, fragment identifiers are meaningless,
SHOULD NOT be used on 'mailto' URIs, and SHOULD be ignored upon
resolution." because fragments are outside of the scope of an URI/
IRI scheme definition.
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Various minor tweaks and fixes.
Fixed spelling of Pete Resnick's name (see
http://www.rfc-editor.org/errata_search.php?rfc=6068&eid=3265).
10.2. Changes from -02 to -03
Introduced non-ASCII text in author names and examples for better
understanding and as a trial for future draft/rfc formats.
Split "Main Changes" and changes by draft number so that the
former can be kept, but the later removed when moving to
publication.
Fixed title of RFC 6068.
Various minor tweaks and fixes.
10.3. Changes from -01 to -02
TODO: Change syntax definition to be in terms of IRI syntax, not
URI syntax.
Split up the Syntax section into subsections.
Added "/" and "?" back to some-delims, because they are allowed in
query parts.
Updated references.
10.4. Changes from -00 to -01
Updated references.
Removed RFC Editor note for updating reference to RFC3987.
Depending on how the documents progress, this will be unnecessary
or will happen automatically.
Minor editorial tweaks.
10.5. Changes from RFC 6068 to -00
Changed title and various other places to also refer to IRIs.
Allowed UTF-8/percent-encoding in <local-part-enc>, to be used for
EAI email addresses.
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Updated syntax to use "-enc" prefix in some places.
Added MUST for using UTF-8 in <hfvalue>.
Added a new subsection with EAI-only examples.
Updated references.
Updated first author's address.
11. Acknowledgments
This document was derived from [RFC6068]; the acknowledgments from
that specification and its predecessor still apply.
Valuable input on this document was received from (in no particular
order): Shawn Steele, Frank Ellermann, John Klensin, Yangwoo Ko, John
Levine, and Roy Fielding.
12. References
12.1. Normative References
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[RFC2047] Moore, K., "MIME Part Three: Message Header Extensions for
Non-ASCII Text", RFC 2047, November 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864,
September 2004.
[RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource
Identifiers (IRIs)", RFC 3987, January 2005.
[RFC5322] Resnick, P., "Internet Message Format", RFC 5322,
October 2008.
[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, August 2010.
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[RFC5891] Klensin, J., "Internationalized Domain Names in
Applications (IDNA): Protocol", RFC 5891, August 2010.
[RFC6532] Yang, A., Steele, S., and N. Freed, "Internationalized
Email Headers", RFC 6532, February 2012.
[STD63] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[STD66] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[STD68] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
12.2. Informative References
[RFC2324] Masinter, L., "Hyper Text Coffee Pot Control Protocol
(HTCPCP/1.0)", RFC 2324, April 1998.
[RFC4395bis]
Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
Registration Procedures for New URI/IRI Schemes",
draft draft-ietf-iri-4395bis-irireg-04, December 2011.
[RFC6068] Duerst, M., Masinter, L., and J. Zawinski, "The 'mailto'
URI Scheme", RFC 6068, October 2010.
[RFC6530] Klensin, J. and Y. Ko, "Overview and Framework for
Internationalized Email", RFC 6530, February 2012.
Authors' Addresses
Martin J. Duerst (Note: Please write "Duerst" with u-umlaut wherever
possible, for example as "Dürst" in XML and HTML.)
Aoyama Gakuin University
5-10-1 Fuchinobe
Chuo-ku
Sagamihara, Kanagawa 252-5258
Japan
Phone: +81 42 759 6329
Fax: +81 42 759 6495
Email: duerst@it.aoyama.ac.jp
URI: http://www.sw.it.aoyama.ac.jp/D%C3%BCrst/
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Larry Masinter
Adobe Systems Incorporated
345 Park Ave
San Jose, CA 95110
USA
Phone: +1-408-536-3024
Email: LMM@acm.org
URI: http://larry.masinter.net/
Jamie Zawinski
DNA Lounge
375 Eleventh Street
San Francisco, CA 94103
USA
Email: jwz@jwz.org
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