Osterman Research , and has this interesting statistic.
Eighty-four percent of organizations have had a virus, worm or Trojan horse successfully infiltrate their network through email, while 54% of organizations have had such a threat successfully enter their network through the Web. However, only about one in five organizations have been infected by a public instant messaging (IM) network worm or virus.
Through email? To me, this highlights how dangerous it is to rely on only one vendor for your email antivirus.
Use a multi-engine approach. Our own email security product for Exchange, uses multiple antivirus engines, so of course I’m biased here.
But so do others — Microsoft Antigen and even GFI. You can also use one AV product on the Exchange server, and another at the gateway. But relying on one engine alone seems to me to be asking for trouble.