[Dovecot] Message mixing after switchover from mbox to maildir

[Andrey Falko]

Hi everyone,

Here is the story. We are running Redhat Enterprise Linux 4, and were 
using Dovecot .99.x . At
one point, we chose to switch from mbox to maildir (and still use 
Dovecot). After the switchover
our users reported a bug when using Thunderbird:

"A new behavior that I have observed a couple of times is that the new IMAP
server confuses email headers with content. E.g., I have an email from 
Person X,
but when I go to view it, the contents is just a spam body from an 
adjacent header.
With this specific bug, adjacent spams are also running into other 
bodies. This
occurs I'd say once every hundred messages. Other appearances of this 
bug are
with adjacent messages concatenated.

I'm not sure how to explain this, maybe what happens is that the new IMAP
server confuses requests and delivers the wrong message bodies to the 
client,
which get cached.

This could in some circumstances be more than an annoyance, e.g., with
confidential emails inadvertently getting picked up in replies to people
outside the company."

We proceeded to update Dovecot to the latest available version 
(1.0.0-rc25).
However, despite that, our users still report the same bug:

"This bug still persists. In particular, I just (after the new version 
was applied)
clicked on an email from Person X, and Thunderbird displayed an email from
Person Y that I had just replied to. Note that the email from Y was not
adjacent to the one from X (at least, in the temporal ordering)."

I have not been able to reproduce the bug myself. Can anyone think of
where we should start debugging?

Best regards,
Andrey Falko