Reappearing emails - IMAP trace

[Timo Sirainen]

On 09 Mar 2016, at 03:57, Ron Cleven <Ron at Cleven.com> wrote:
> 
> A few days back, I sent an overview of this problem, but received no responses.   Since then, I have run dozens of traces to isolate the problem, difficult because there are timing issues involved.  I have finally nailed it down.  If this is not the proper place to report such bugs or if someone knows that this bug has been fixed, please let me know.  As I noted in my earlier post, we have been running Dovecot 2.2.10 with a pair of CentOS 7 boxes with replications for the past year.  We have been quite happy with the performance and reliability.
> 
> Recently we received a report that emails could reappear in the INBOX after being deleted.  After running a pile of traces, I determined that the problem was strangely related to replications.  For the purposes of this discussion, I will refer to the two symmetric replicating servers as A and B.  Further, let us assume that during "normal" operation, all the emails are delivered to A via SMTP and are replicated to B.  Under those assumptions, if the IMAP user connects to A (where the messages were originally delivered), there is no problem, at least no problem I was able to find.  The problem I am describing only arises if the IMAP user connects to B.  Connecting to B has never presented any other problems that I am aware of.
> 
> The test for which I have provided the trace starts with a test mailbox containing only 3 unread messages in the INBOX.  Moving 1 of the unread messages to Trash is all that is needed to reproduce the problem.  Remember this is ONLY a problem if the IMAP sessions do not connect to the server to which the messages were originally delivered.  Also, I found that there is a timing window.  The critical IMAP commands are:
> 
>   UID STORE xxx +FLAGS.SILENT (\Seen)
>   UID MOVE xxx Trash
> 
> If you introduce a large enough delay (I arbitrarily chose 5 seconds) between those two commands, there is no problem. Presumably this has to do with the two boxes syncing up some critical data structure.

What mailbox format do you use? Are you able to reproduce this by running doveadm sync commands manually instead of letting replication do it? For example:

 - doveadm sync -s "" -d -u user at domain > state
 - Run the UID STORE & UID MOVE
 - doveadm sync -s "`cat state`" -d -u user at domain

There have been some fixes, especially recently https://github.com/dovecot/core/commit/950a6e61d6c2dac961ce031bdd8b2895bc32b827 sounds a bit similar although I don't really see how it would apply here. Would be a good idea to try anyway with v2.2.22.rc1 (which seems to be stable enough that I'll make v2.2.22 release soon).

Anyway, I attempted a few times to reproduce it with your test but wasn't able to.