Due to the critical nature of our email usage a major virus outbreak on our Exchange servers would probably cost me my job. So to help me sleep easier at night I use layers of defence. We run one anti-virus product on our MailSweeper gateway servers and a product from a different vendor on all of our internal Exchange servers. The concept of using different products is if one vendor doesn’t have a definition available to detect a certain virus the other vendor might. This layered approach gives us a fighting chance if a virus gets past MailSweeper or hits us from the inside via a webmail service.
As additional precaution we set the automatic definition updates to be as frequent as possible and also block any executable attachments (internal & external).