Free Software: clamav. Works surprisingly well, community maintained, many people feel that it doesn't provide the response times to new viruses that proprietary solutions do.
Proprietary Software: NOD32. Fast, effective, and fairly malleable. I'd recommend it.
I've used NOD32 and Kaspersky (KAV) and found Kaspersky to be superior overall.
Anyway, YMMV. Web sites are here:
http://www.nod32.com/
http://www.kasperskylabs.com/
The NOD32 software makes you pay for a per-user license to use it on a mail server. The Kaspersky labs software is a single-server license for as many users as you want.
-- Del
-- SLUG - Sydney Linux User's Group - http://slug.org.au/ More Info: http://lists.slug.org.au/listinfo/slug
