One of our Outlook users can't send big attachements any more and for a few
days the 'Sent' folder on the server is not synced with the 'Sent Items' folder
in Outlook any more.

Apparently it started with one message that failed to be sent (attachement about 6MB) a few weeks ago. The user's system was rebuilt and after that no
problems with Outlook and Zimbra where reported. Last week the user tried to
sent another mail (2MB attachement) which got stuck again. Even after the
mail was removed from the Outbox in Outlook the server kept showing errors
of failed file uploads. Example:

2009-07-20 12:44:53,514 INFO [btpool0-1285] [name=user@example.com;mid=12;ip=;ua =Zimbra-ZCO/5.0.2992.16 (6.0.6001 Service Pack 1;; en-GB);] FileUploadServlet - File upload failed
2009-07-20 12:44:53,514 INFO [btpool0-1285] [name=user@example.com;mid=12;ip=;ua =Zimbra-ZCO/5.0.2992.16 (6.0.6001 Service Pack 1;; en-GB);] FileUploadServlet - Ignoring error that occurred while reading the end of the client request: org.mortbay.jetty.EofException

We tried to delete the profile and let Outlook resync the account. This
stopped the existing error messages but the user still can't send attachments. I could reproduce the error on sending a big attachment with
a different user account on a different machine; a small attachemnt did
work, though. The error message from Outlook is "Network connection failure". Sending large attachments via web interface or IMAP works
without problems.

The first user now also does not see sent emails in his 'Sent' folder on
the server. The mails are sent out, appear in the 'Sent Items' folder in
Outlook but they do not appear in the Zimbra web interface. This did not
happen on the other account, so I believe this is profile/account related.

The environment is:

ZCS NE 5.0.16/5.0.18 on CentOS 5.3 (both with the same error)
Connector versions: 5.0.5/5.0.16/5.0.18 (all have this problem)
Outlook 2007 on Window Vista 64bit

I have seen a few reports of problems with attachments in this forum
but none of them seems to fit this situation. In particular, there is
hardly any information in the logs.