Antivirus software is a necessary annoyance, required because of the (essentially) Wild West character of Internet connectivity.
Although critically important, when it comes to Exchange servers AV applications shouldn’t be deployed without regard for the messaging system’s behaviors and dependencies.
Fortunately, Microsoft provides a solid guide to using file-level AV scanning on Exchange 2010 servers.
File-level scanners are frequently used. However, if they are configured incorrectly, they can cause problems in Exchange 2010. There are two types of file-level scanners:
- Memory-resident file-level scanning refers to a part of file-level antivirus software that is loaded in memory at all times. It checks all the files that are used on the hard disk and in computer memory.
- On-demand file-level scanning refers to a part of file-level antivirus software that you can configure to scan files on the hard disk manually or on a schedule. Some versions of antivirus software start the on- demand scan automatically after virus signatures are updated to make sure that all files are scanned with the latest signatures.
full here at Technet…