the X-OfflineIMAP header

Dan Christensen jdc at
Thu Nov 25 16:25:00 GMT 2010

Two questions about this header, when doing IMAP-->IMAP syncs:

1) If an article arrives at the remote IMAP server and is synced to
the local IMAP server, the local copy gets an X-OfflineIMAP header
(so that offlineimap can figure out the UID of the local copy)
while the remote copy remains unchanged.  This makes sense.

But when an article arrives at the local IMAP server and is synced to
the remote server, both copies get an X-OfflineIMAP header.  And this
is a problem, because in order to do this, offlineimap must delete the
local message and create a new message (with a new UID).  This causes
some confusion with my mail client, since it often happens while I'm
viewing the message, so it vanishes and then appears as a different
message.  And it seem unnecessary, since offlineimap already knows
the UID for the local message.

Is this easy to fix?

2) For IMAP servers that support UIDPLUS, it shouldn't be necessary to
insert the X-OfflineIMAP header at all, since they return the UID of
the APPENDed message using the APPENDUID response code:

For example, 

1 APPEND "test" () {87}
+ OK
Date: Thu, 25 Nov 2010 11:18:01 -0400 (EST)
From: Dan <jdc at xxxxxx>
Subject: test


1 OK [APPENDUID 1254248544 10732] Append completed.

The number 10732 is the UID of the newly created message.  No need
to alter the message with a header or to issue a separate SEARCH


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