I recieved this from one of the sites I subscribe to and I thought I'd share it here.
FAQ: HOW CAN I DETERMINE WHETHER MY ANTIVIRUS PRODUCT IS PROTECTING MY
EMAIL FROM ALL THREATS?
( contributed by John Savill, http://www.windows2000faq.com )
Although it's almost impossible to completely secure your email, you
can check for known threats. A free test zone is available online at the
URL below. If your antivirus product catches all the test viruses, your
systems are protecting you from all known viruses.
To test goto -> http://www.gfi.com/emailsecuritytest
I tried it with one of my web-based e-mail account and it did send back a bunch of info I haven't gone through yet.
Give it a try if you want.