I'm having a similar problem with one client (but have another client where Outlook is also used, and don't have this issue). I have a problem understanding how the client can hang the server process(es), too. Restarting the network services doesn't help - they don't correctly restart, so remote access is down at this point - the server has to be restarted to resolve, and there are no errors in the logs.
The only difference I see is that, in the problem case, I upgraded from 5.6 to 6.0, but neglected to uninstall the Secure Email RPMs before upgrading - I did it afterwards, then applied the 6.0 versions.
Can anyone suggest why it is hanging?
Thanks,
Des