Internet DRAFT - draft-melnikov-imap-mdn

draft-melnikov-imap-mdn









Internet Draft: MDN profile for IMAP                         A. Melnikov
Document: draft-melnikov-imap-mdn-05.txt   ACI Worldwide/MessagingDirect
Expires: June 2003                                         December 2002
Intended category: BCP

                          MDN profile for IMAP

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.  Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups.  Note that other groups may also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
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   The list of current Internet-Drafts can be accessed at
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   A revised version of this draft document will be submitted to the RFC
   editor as a BCP (Best Current Practive) document. Discussion and
   suggestions for improvement are requested, and should be sent to the
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Copyright Notice

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

Table of Contents

   1.    Abstract......................................................2
   2.    Conventions Used in this Document.............................2
   3.    Introduction and Overview.....................................3
   4.    Client behavior...............................................3
   4.1.  Client behavior when receiving a message......................5
   4.2.  Client behavior when copying a message........................5
   4.3.  Client bahavior when sending a message........................5
   4.4.  Client bahavior when saving a temporary message...............5



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   5.    Server behavior...............................................6
   5.1.  Server that supports arbitrary keywords.......................6
   5.2.  Server that supports only $MDNSent keyword....................6
   5.3.  Interaction with IMAP ACL extension...........................6
   6.    Examples......................................................7
   7.    Security Considerations.......................................8
   8.    Formal Syntax.................................................8
   9.    Acknowledgments...............................................8
   10.   Normative References..........................................9
   11.   Author's Address..............................................9
   12.   Full Copyright Statement.....................................10

1.   Abstract

   Message Disposition Notification [MDN], also known as
   'acknowledgements' or 'receipt notifications' is one of the widely
   used features of X.400 and the proprietary 'LAN-based' messaging
   systems. [MDN] defines how this functionality may be supported by
   Internet Mail, however it doesn't describe how multiple Mail User
   Agents (MUAs) may use MDN together with the Internet Message Access
   Protocol [IMAP4].

   This document describes the Best Current Practice of using MDN with
   [IMAP4] and should be considered as guidelines for implementers of
   the Internet Message Access Protocol [IMAP4] that want to add MDN
   support to their products.


2.   Conventions Used in this Document

   "C:" and "S:" in examples show lines sent by the client and server
   respectively.

   The keywords "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" in
   this document when typed in uppercase are to be interpreted as
   defined in "Key words for use in RFCs to Indicate Requirement Levels"
   [KEYWORDS].














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3.   Introduction and Overview

   This memo defines an additional [IMAP4] mailbox keyword that allows
   multiple Mail User Agents (MUAs) to know if a requested receipt
   notification was sent or not.

   Message Disposition Notification [MDN] does not require any special
   support of IMAP in the case where a user has access to the mailstore
   only from one computer and using a single MUA. In this case the MUA
   behaves as described in [MDN], i.e., the MUA performs automatic
   processing and generates corresponding MDNs, then it performs
   requested action and, with the user's permission, sends appropriate
   MDNs. The MUA will not send MDN twice, because the MUA keeps track of
   sent notifications in a local configuration. However that doesn't
   work when IMAP is used to access the same mailstore from different
   locations or using different MUAs.

   This document defines a new special purpose mailbox keyword $MDNSent
   that must be used by MUAs. It doesn't define any new command or
   response for IMAP, but describes a technique that MUAs should use to
   achieve interoperability.

   When a client opens a mailbox for the first time it verifies that the
   server is capable of storing the $MDNSent keyword by examining the
   PERMANENTFLAGS response code. In order to support MDN in IMAP a
   server MUST support either the $MDNSent keyword, or arbitrary message
   keywords.


4. Client behavior

   The use of IMAP requires few additional steps in mail processing on
   the client side. The following timeline modifies the timeline found
   in Section 4 of [MDN].

   -- User composes message

   -- User tells MUA to send message

   -- MUA passes message to MSA (original recipient information passed
      along). MUA [optionally] saves message to a folder for sent mail
      with $MDNSent flag set.

   -- MSA sends message to MTA.

   -- Final MTA receives message.

   -- Final MTA delivers message to MUA (possibly generating DSN).



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   -- MUA logs into IMAP server, opens mailbox, verifies if mailbox can
      store $MDNSent keyword by examining PERMANENTFLAGS response.

   -- MUA performs automatic processing and generates corresponding MDNs
      ("dispatched", "processed", "deleted", "denied" or "failed"
      disposition type with "automatic-action" and "MDN-sent-
      automatically" disposition modes) for messages that don't have
      neither $MDNSent keyword, nor \Draft flag set. (*)

   -- MUA sets $MDNSent keyword for every messages that required an
      automatic MDN to be sent, whether the MDN was sent or not.

   -- MUA displays list of messages to user.

   -- User selects a message and requests that some action be performed
      on it.

   -- MUA performs requested action and, with user's permission, sends
      appropriate MDN ("displayed", "dispatched", "processed",
      "deleted", "denied" or "failed" disposition type with "manual-
      action" and "MDN-sent-manually" or "MDN-sent-automatically"
      disposition mode).

   -- MUA sets $MDNSent keyword for all message for which user confirmed
      the dispatching of disposition (or explicitly prohibited to do
      so).

   -- User possibly performs other actions on message, but no further
      MDNs are generated.

  (*) Note: MUA MUST NOT use \Recent flag as an indicator, that it
      should send MDN, because according to [IMAP4] "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". Thus using \Recent as an indicator will cause unpredictable
      client behavior with different IMAP4 servers. However the client
      MAY use \Seen flag as one of indicators that MDN must not be sent.
      Client MUST NOT use any other standard flags like \Draft or
      \Answered to indicate that MDN was previously sent, because they
      have different well known meaning.  In any case, in the presence
      of $MDNSent keyword, the client MUST ignore all other flags or
      keywords for the purpose of generating an MDN and MUST NOT send
      the MDN.

   When the client opens a mailbox for the first time it must verify
   that the server supports or $MDNSent keyword, or arbitrary message
   keywords by examining PERMANENTFLAGS response code.



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   The client MUST NOT try to set $MDNSent keyword if the server is
   incapable of storing it permanently.

   The client MUST be prepared to receive NO from the server as the
   result of STORE $MDNSent when the server advertises the support of
   storing arbitrary keywords, because the server may limit the number
   of message keywords it can store in a particular mailbox. Client
   SHOULD NOT send MDN if it fails to store $MDNSent keyword.

   Once $MDNSent keyword is set it MUST NOT be unset by a client. The
   client MAY set $MDNSent keyword when user denied sending the
   notification. This prohibits all other MUA from sending MDN for this
   message.


4.1. Client behavior when receiving a message

   The client MUST NOT send MDN if a message has $MDNSent keyword set.
   It also MUST NOT send MDN if a message has \Draft flag, because some
   clients use this flag to mark message as uncomplete.

   See timeline in section 4 for details on client bahavior when
   receiving a message.


4.2. Client behavior when copying a message

   The client SHOULD verify that $MDNSent is preserved on a COPY
   operation. Furthermore when message is copied between servers with
   APPEND command client MUST set correctly the $MDNSent keyword.

4.3. Client bahavior when sending a message

   When saving a sent message to any folder client MUST set $MDNSent
   keyword to prevent another client from sending MDN for the message.


4.4. Client bahavior when saving a temporary message

   When saving an unfinished message to any folder client MUST set
   $MDNSent keyword to prevent another client from sending MDN for the
   message.









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5. Server behavior

   Server implementors that want to follow this specification must
   insure that their server complies with eiter section 5.1 or section
   5.2. If the server also supports IMAP [ACL] extension it MUST also
   comply with the section 5.3.


5.1. Server that supports arbitrary keywords

   No changes required from the server to make it compatible with the
   extension described in this document if it supports arbitrary
   keywords.


5.2. Server that supports only $MDNSent keyword

   Servers that support only the $MDNSent keyword MUST preserve it on
   COPY operation. It is also expected that a server that supports
   SEARCH <flag> will also support SEARCH KEYWORD $MDNSent.


5.3. Interaction with IMAP ACL extension

   Any server that conforms to either 5.1 or 5.2 and also supports IMAP
   [ACL] extension SHOULD preserve $MDNSent keyword on COPY even if the
   client doesn't have 'w' right. This will prevent generation of a
   duplicated MDN for the same message. Note that the server still MUST
   check if the client has rights to perform COPY operation on a message
   according to [ACL].





















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6.   Examples

   1). MUA opens mailbox for the first time.

    a). The server supports storing of arbitrary keywords

     C: a100 select INBOX
     S: * FLAGS (\Flagged \Draft \Deleted \Seen)
     S: * OK [PERMANENTFLAGS (\Flagged \Draft \Deleted \Seen \*)]
     S: * 5 EXISTS
     S: * 3 RECENT
     S: * OK [UIDVALIDITY 894294713]
     S: a100 OK [READ-WRITE] Completed

    b). The server supports storing of $MDNSent keyword

     C: a100 select INBOX
     S: * FLAGS (\Flagged \Draft \Deleted \Seen $MDNSent)
     S: * OK [PERMANENTFLAGS (\Flagged \Draft \Deleted \Seen $MDNSent)]
     S: * 5 EXISTS
     S: * 3 RECENT
     S: * OK [UIDVALIDITY 894294713]
     S: a100 OK [READ-WRITE] Completed

    2). The MUA successfully sets $MDNSent keyword

     C: a200 STORE 4 +FLAGS ($MDNSent)
     S: * 4 FETCH (FLAGS (\Flagged \Seen $MDNSent))
     S: * FLAGS ($MDNSent \Flagged \Deleted \Draft \Seen)
     S: * OK [PERMANENTFLAGS ($MDNSent \Flagged \Deleted \Draft \Seen \*)]
     S: a200 OK STORE completed

    3). The server refuses to store $MDNSent keyword

     C: a200 STORE 4 +FLAGS ($MDNSent)
     S: a200 NO STORE failed : no space left to store $MDNSent keyword















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    4). All clients and servers MUST treat $MDNSent keyword as case
        insensitive in all operations, as stated in [IMAP].

     C: a300 FETCH 1:* FLAGS
     S: * 1 FETCH (FLAGS (\Seen))
     S: * 2 FETCH (FLAGS (\Answered \Seen $MdnSENt))
     S: * 3 FETCH (FLAGS ())
     S: * 4 FETCH (FLAGS (\Flagged \Seen $MdnSENT))
     S: * 5 FETCH (FLAGS ($MDNSent))
     S: * 6 FETCH (FLAGS (\Recent))
     S: a300 OK FETCH completed
     C: a400 SEARCH KEYWORDS $mdnsent
     S: * SEARCH 2 4 5
     S: a400 OK SEARCH completed


7.   Security Considerations

   There are no known security issues with this extension, not found in
   [MDN] and/or [IMAP4].

   Section 5.3 changes ACL checking requirements on a IMAP server that
   implements IMAP [ACL] extension.


8.   Formal Syntax

   The following syntax specification uses the augmented Backus-Naur
   Form (BNF) notation as specified in [RFC-822] as modified by [IMAP4].
   Non-terminals referenced but not defined below are as defined by
   [IMAP4].

   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.

   flag_keyword    ::= "$MDNSent" / other_keywords

   other_keywords  ::= atom


9.   Acknowledgments

   This document is the product of discussions that took place on the
   IMAP mailing list. Special gratitude to Cyrus Daboo and Randall
   Gellens for reviewing the document.




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10.  Normative References

   [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
   Requirement Levels", RFC 2119, March 1997.

   [MDN] Fajman, R., "Message Disposition Notifications", RFC 2298,
   National Institutes of Health, March 1998.

   [IMAP4] Crispin, M., "Internet Message Access Protocol - Version
   4rev1", draft-crispin-imapv-20.txt, University of Washington,
   December 1996.

   [ACL] Myers, J., "IMAP4 ACL extension", RFC 2086, Carnegie Mellon
   University, January 1997.

11.  Author's Address

   Alexey Melnikov
   ACI Worldwide/MessagingDirect
   Address: 22 The Quadrant, Richmond, Surrey, United Kingdom, TW9 1BP
   Phone: +44 20 8332 4508

   Email: mel@messagingdirect.com




























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12.  Full Copyright Statement

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















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