You want to know a method of testing the capabilities of Symantec Mail Security for Microsoft Exchange (SMSMSE) to detect viruses.
An easy way to test whether SMSMSE is catching viruses is to use the eicar antivirus test string. You can download this file from www.eicar.org.
To test the antivirus software on your Microsoft Exchange server, send an email from one user account to another, with the eicar antivirus test file attached. The attachment should be quarantined, or the message dealt with according to any custom configuration of the Antivirus policy.