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RFC5162, "IMAP4 Extensions for Quick Mailbox Resynchronization", March 2008

Note: This RFC has been obsoleted by RFC7162

Source of RFC: lemonade (app)

Errata ID: 1808

Status: Verified
Type: Technical

Reported By: Timo Sirainen
Date Reported: 2009-07-14
Verifier Name: Alexey Melnikov
Date Verified: 2009-07-18

Section 3.4 says:

   If at least one message got expunged, the server MUST send
   the updated per-mailbox modification
   sequence using the HIGHESTMODSEQ response code (defined in
   [CONDSTORE]) in the tagged OK response.

      Example:    C: A202 CLOSE
                  S: A202 OK [HIGHESTMODSEQ 20010715194045319] done

It should say:

   The server MUST NOT send the updated per-mailbox modification
   sequence using the HIGHESTMODSEQ response code (defined in
   [CONDSTORE]) in the tagged OK response, as this might cause loss of
   synchronization on the client.

      Example:    C: A202 CLOSE
                  S: A202 OK done

Notes:

Rationale:

The HIGHESTMODSEQ can't be used reliably unless server sends to client all changes done by other clients. Even then it's difficult for both clients and servers to implement this. For example:

C1: 2 STORE 1 +FLAGS.SILENT \Deleted
S1: * 1 FETCH (MODSEQ 1)
S1: 2 OK

C2: 1 STORE 2 +FLAGS.SILENT \Deleted
S1: * 2 FETCH (MODSEQ 2)
S2: 1 OK

C1: 3 CLOSE
S1: 3 [HIGHESTMODSEQ 3]

The client probably thought that only message 1 was expunged, so it
doesn't register the second expunge. And it probably never will if it
uses QRESYNC to find out only about new expunges.

And even worse example would be if the second client had also removed
the \Deleted flag from message 1. Then the first client would have
registered wrong message to be expunged.


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