IMAP4 Multimailbox SEARCH Extension
draft-ietf-morg-multimailbox-search-02

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Abstract

The IMAP4 specification allows the searching only of the selected mailbox. A user often wants to search multiple mailboxes, and a client that wishes to support this must issue a series of SELECT and SEARCH commands, waiting for each to complete before moving on to the next. This extension allows a client to search multiple mailboxes with one command, limiting the round-trips and waiting for various searches to complete, and not requiring disruption of the currently selected mailbox. This also uses MAILBOX and TAG fields in ESEARCH responses, allowing a client to pipeline the searches if it chooses.

Note

A revised version of this draft document will be submitted to the RFC editor as a Proposed Standard for the Internet Community. Discussion and suggestions for improvement are requested, and should be sent to morg@ietf.org.

Table of Contents

1.  Conventions used in this document

2.  Extended SEARCH/UID SEARCH command

3.  Example

4.  Formal Syntax

5.  Security Considerations

6.  IANA Considerations

7.  Acknowledgements

8.  Normative References

§  Authors' Addresses

1.  Conventions used in this document

In examples, "C:" indicates lines sent by a client that is connected to a server. "S:" indicates lines sent by the server to the client.

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 RFC 2119 [Kwds] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).

2.  Extended SEARCH/UID SEARCH command

Arguments:

OPTIONAL source options OPTIONAL result options
OPTIONAL charset specification (see [CHARSET] (Freed, N. and J. Postel, “IANA Charset Registration Procedures,” October 2000.))
searching criteria (one or more)

Responses:

REQUIRED untagged response: SEARCH or ESEARCH

Result:

OK - search completed NO - error: cannot search that charset or criteria
BAD - command unknown or arguments invalid

This section further updates definition of the SEARCH command described in section 2.6.1 of [IMAPABNF] (Melnikov, A. and C. Daboo, “Collected Extensions to IMAP4 ABNF,” April 2006.) (initially described in section 6.4.4 of [IMAP] (Crispin, M., “Internet Message Access Protocol - Version 4rev1,” March 2003.).

The SEARCH command is extended to allow for optional source and result options. This document does not define any result options. A server that supports this extension includes "MSEARCH" in its IMAP capability string.

Unless specified otherwise by a description of a result option, in the presence of a search source option the server MUST return ESEARCH responses instead of the corresponding SEARCH responses. Because message numbers are not useful for mailboxes that are not selected, each ESEARCH response MUST return information about UIDs, not message numbers, regardless of whether it is in response to a SEARCH or a UID SEARCH command. In particular, the responses MUST contain the UID indicator.

Presence of a source option in absence of a result option implies the "ALL" result option (see [ESEARCH] (Melnikov, A. and D. Cridland, “IMAP4 Extension to SEARCH Command for Controlling What Kind of Information Is Returned,” November 2006.)).

Source options describe which mailboxes must be searched for messages. Note that a SEARCH/UID SEARCH command with source options doesn't affect which mailbox, if any, is currently selected, regardless of which mailboxes are searched. For each mailbox satisfying the source options, a single ESEARCH response MUST be returned if any messages in that mailbox match the search criteria. An ESEARCH respoonse SHOULD NOT be returned for mailboxes that contain no matching messages. Each ESEARCH response MUST contain the MAILBOX, TAG, and UIDVALIDITY correlators. Correlators allow clients to issue several SEARCH/UID SEARCH commands at once (pipelined). The server MAY perform pipelined searches in parallel; or it MAY instead serialize them.

The source options, if present, MUST contain a mailbox specifier as defined in the IMAP NOTIFY extension [NOTIFY] (Gulbrandsen, A., King, C., and A. Melnikov, “The IMAP NOTIFY Extension,” February 2009.), section 6 (using the "filter-mailboxes" ABNF item), with the following changes:

1. The "selected-delayed" specifier is not valid here.
2. A "subtree-one" specifier is added. The "subtree" specifier results in a search of the specified mailbox and all selectable mailboxes that are subordinate to it, through an indefinitely deep hierarchy. The "subtree-one" specifier results in a search of the specified mailbox and all selectable child mailboxes, one hierarchy level down.

If "subtree" is specified, the server MUST defend against loops in the hierarchy (for example, those caused by recursive file-system links within the message store). The server SHOULD do this by keeping track of the mailboxes that have been searched, and terminating the hierarchy traversal when a repeat is found. If it can not do that, it MAY do it by limiting the hierarchy depth.

If the source options are not present, the value "selected" is assumed -- that is, only the currently selected mailbox is searched.

If the source options include (or default to) "selected", the IMAP session MUST be in "selected" state. If the source options specify other mailboxes and NOT "selected", then the IMAP session MUST be in "selected" or "authenticated" state. If the session is not in a correct state, the SEARCH command returns a "BAD" result.

If the server supports the ACL [ACL] (Melnikov, A., “IMAP4 Access Control List (ACL) Extension,” December 2005.) extension, then the logged in user is required to have the 'r' right for each mailbox she wants to search. Mailboxes matching the source options for which the logged in user has no 'r' right MUST be ignored by a multimailbox search. In particular, ESEARCH responses MUST NOT be returned for those mailboxes.

[CONTEXT] (Cridland, D. and C. King, “Contexts for IMAP4,” July 2008.) [NOTIFY] (Gulbrandsen, A., King, C., and A. Melnikov, “The IMAP NOTIFY Extension,” February 2009.) [anchor3] (Interaction with CONTEXT (RFC 5267) needs to be defined. Also, UPDATE option draft-ietf-lemonade-imap-notify might have to be prohibited when both CONTEXT and this extension are used. We might also have to consider interaction with ESEARCH, RFC 4731.)

3.  Example

C: tag1 SEARCH IN ((mailboxes "folder1" subtree "folder2")) unseen
C: tag2 SEARCH IN ((mailboxes "folder1" subtree-one "folder2")) subject "chad"
S: * ESEARCH (TAG "tag1" MAILBOX "folder1" UIDVALIDITY 1) UID ALL 4001,4003,4005,4007,4009
S: * ESEARCH (TAG "tag2" MAILBOX "folder1" UIDVALIDITY 6789023554) UID ALL 195001:195004,169788
S: * ESEARCH (TAG "tag1" MAILBOX "folder2/banana" UIDVALIDITY 503) UID ALL 3002,4004
S: * ESEARCH (TAG "tag1" MAILBOX "folder2/peach" UIDVALIDITY 3) UID ALL 921691
S: tag1 OK done
S: * ESEARCH (TAG "tag2" MAILBOX "folder2/salmon" UIDVALIDITY 1111111) UID ALL 50003,50006,50009,50012
S: tag2 OK done

4.  Formal Syntax

The following syntax specification uses the augmented Backus-Naur Form (BNF) as described in [ABNF] (Crocker, D., Ed. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” January 2008.). Terms not defined here are taken from [IMAP] (Crispin, M., “Internet Message Access Protocol - Version 4rev1,” March 2003.), [NOTIFY] (Gulbrandsen, A., King, C., and A. Melnikov, “The IMAP NOTIFY Extension,” February 2009.), or [IMAPABNF] (Melnikov, A. and C. Daboo, “Collected Extensions to IMAP4 ABNF,” April 2006.).

filter-mailboxes-other =/

("subtree-one" SP one-or-more-mailbox) ; Update definition from RFC 5465 [NOTIFY] (Gulbrandsen, A., King, C., and A. Melnikov, “The IMAP NOTIFY Extension,” February 2009.)
; Add new "subtree-one" selector.

filter-mailboxes-selected =

"selected" ; Update definition from RFC 5465 [NOTIFY] (Gulbrandsen, A., King, C., and A. Melnikov, “The IMAP NOTIFY Extension,” February 2009.)
; We forbid the use of "selected-delayed".

one-correlator =

("TAG" SP tag-string) / ("MAILBOX" SP astring) / ("UIDVALIDITY" SP nz-number) ; Each correlator MUST appear exactly once

scope-option =

scope-option-name [SP scope-option-value] ; No options defined here. Syntax for future extensions.

scope-option-name =

tagged-ext-label ; No options defined here. Syntax for future extensions.

scope-option-value =

tagged-ext-val ; No options defined here. Syntax for future extensions.

scope-options =

scope-option *(SP scope-option) ; A given option may only appear once
; No options defined here. Syntax for future extensions.

search =

"SEARCH" [SP search-source-opts] [SP search-return-opts] SP search-program ; Updates definition in RFC 4466 [IMAPABNF] (Melnikov, A. and C. Daboo, “Collected Extensions to IMAP4 ABNF,” April 2006.)

search-correlator =

SP "(" one-correlator *(SP one-correlator) ")" ; Updates definition in RFC 4466 [IMAPABNF] (Melnikov, A. and C. Daboo, “Collected Extensions to IMAP4 ABNF,” April 2006.)

search-source-opts =

"IN" SP "(" source-mbox [SP "(" scope-options ")"] ")"

source-mbox =

filter-mailboxes *(SP filter-mailboxes) ; filter-mailboxes is defined in RFC 5465 [NOTIFY] (Gulbrandsen, A., King, C., and A. Melnikov, “The IMAP NOTIFY Extension,” February 2009.)
; See updated definition of filter-mailboxes-other, above.
; See updated definition of filter-mailboxes-selected, above.

5.  Security Considerations

[anchor5] (This needs to be properly written. Notes from minutes of IETF 74, for now...)

Chris suggests shared mailboxes could be used to force spam into search results by owner of shared mailbox. Chris wonders about a parameter that says search only user's own mailboxes (no shared). Cyrus says you can use metadata to tag mailboxes you don't want to search, and use search criteria to exclude them. The "personal" selector may work for this, as well.

Suggestions to add EXCLUDE clause (with a nested search criteria) for Trash, e.g.

Suggestions to use metadata tags to mark those mailboxes that you want to (not) search

6.  IANA Considerations

IMAP4 capabilities are registered by publishing a standards track or IESG approved experimental RFC. The registry is currently located here:

   http://www.iana.org/assignments/imap4-capabilities

This document defines the IMAP capability "MSEARCH", and IANA is asked to add it to the registry.

7.  Acknowledgements

The authors gratefully acknowledge feedback provided by Peter Coates and Arnt Gulbrandsen.

8. Normative References

Authors' Addresses