We don't have the Messaging Security component of Worry-Free Business Security installed on the server though. And we aren't using the Trend Firewall - so I can't see anything else I can turn off other than the Exclusion folder we have already added to Realtime Antivirus/Antispyware.
I will try turning off completely Realtime Antivirus/Antispyware though temporarily to test if this makes a difference.