mysteries with attachments

[Liutauras Adomaitis]

Hello Kolab users,

I'm fighting very strange problem - attachments are disappearing or
doubled. No ideas how to dig arround...

Explanation:
Some times some users are getting emails without attachments. For
example one internal user sends email to 7 internal recipients with
one attachment. 5 emails are delivered ok, 2 are delivered without
attachment.  Resending email to whose two are ok. Some users sometimes
are receiving emails with two identical files attached. i did not
found circumstances then this happens. Now it seems it is quite
random.
Using Kolab 2.2.2, clients are Outlook XP,2003,2007 and Horde (some
Outlooks are in Lithuanian language). Bynari Insght connector (latest
version)
Kolab started with all users using pop3s, and few weeks ago started to
migrate all to imaps. Using pop3s worked ok, without any mysteries.
users have no quotas enabled yet.

I understand that this might sound a bit strange, but I need some
ideas where to dig
postfix?
cyrus?
amavis?
kolab?
OS (Mandriva 2009.1)?

thank for your time
Liutauras