I am having problems with a client's Exchange server. Symantec Mail Security for Exchange (SMSE) appears to be unable to scan messages periodically. When it happens it starts around 3:30 or 3:45 AM and you can see in the event log this error for every message:
Event ID: 348
SMTP scanning failed on the message with subject: <Subject>. This message has been set as bad mail on the SMTP server.
Live Update for SMSE seems to be running around the same time (3:15 AM) and applying an update, but it doesn't happen after every update so I'm not sure if that is the problem.
The only way I have found to fix the problem is to completely reboot the server. The e-mail that was delivered at that time is lost though and I haven't found a way to retrieve it.