Previous Anti-Virus Methods

Originally, before a VSAPI was introduced for Exchange, vendors created virus-scanning software that used one of two methods out of necessity. In the first method, MAPI was used to log in to and scan Mailboxes for viruses.

Although this method is still supported in Exchange 2003, it is not recommended because the latency between when an email can be scanned and when a user reads an email is great enough to allow infected messages to slip through the scanning process.

The second method of scanning emails for viruses came through an unsupported interface into the Extensible Storage Engine that Exchange uses (basically replacing the ESE .DLL) Over the years, Microsoft has retained its stance that this type of software is unsupported, and if you ever require assistance from Microsoft Support Services, you must disable your virus-scanning software before Microsoft can help you troubleshoot your Exchange installation.

Both of these methods have some serious limitations that could affect the stability of your Exchange 2003 installation and the effectiveness of the virus-scanning application you are trying to implement. Therefore, if you are using a previous version of Exchange with virus software that employs either of these methods, you might want to consider upgrading your anti-virus protection at the same time you upgrade Exchange.