QRESYNC issues

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gds
Posts: 2
Joined: Tue Nov 16, 2021 6:58 pm

QRESYNC issues

Postby gds » Tue Nov 16, 2021 7:48 pm

I've been researching the addition of imap QRESYNC to Thunderbird. I've noticed that Zimbra has some issues that I don't see with other servers like Dovecot or Cyrus which also support QRESYNC.

A problem with Zimbra is that when a lot of messages are imap APPENDED to a mailbox, the UIDs assigned to them are not always consecutive. This causes zimbra to report the missing UIDs as VANISHED on a new imap SELECT of the mailbox due to missing or skipped UIDs. With a large append of 1000's of messages, it appears that Zimbra does not use about every 7th UID, leaving lots of 1 message (1 UID) gaps.

As another example, say the UIDs in mailbox A are initially 1 to 100 and 100 is the highest UID in any mailbox. Then if I APPEND 100 messages to mailbox B, it will assign UIDs 101 to 200 to the messages. Then if I APPEND 100 more messages to mailbox A, they will be assigned UIDs 201 to 300, leaving a "gap" of 100 UIDs in mailbox A. Messages 101:200 in mailbox A will be reported as VANISHED on a new SELECT.

Also, when messages are truly EXPUNGED, it appears the Zimbra does not really respect the MODSEQ supplied to the SELECT command and just reports all missing UIDs as VANISHED and not just those expunged after the supplied MODSEQ.


gds
Posts: 2
Joined: Tue Nov 16, 2021 6:58 pm

Re: QRESYNC issues

Postby gds » Thu Nov 18, 2021 12:14 am

I can fix the small gaps in UID assignment with a change to Thunderbird. It seems that Zimbra does not like email headers sent via imap APPEND that begin with "From ". It causes Zimbra to sometimes ignore the "Date:" header and and also skip UIDs so they are not consecutively assigned. The proposed tb fix can be found here: bug 1741748

I still tend to think that a leading "From " in the imap APPEND messages should just be ignored by Zimbra. I've not noticed this problem with other servers.

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