Have Imail and I use Declude with Mcafee and F Prot for virus scanning. We also have Symantec CE which scans through Outlook.
One virus scanner is not enough. Incredible how many virus attempts are made each day on our system.
I really like Declude, the price seems high for the Pro version, but the use of very cheap virus scan engines make up for it. Setup is easy, as long as you get the newest documentation.
I consider Declude as a necessity. I don't worry about viruses anymore; if something get through the 3 scans, it is beyond anyone's control
Imail is super easy to setup, once your ISP gets your DNS settings correctly set. Imail's tech support was really good