F-Prot Antivirus BSD Mail Servers utilizes the renowned F-Prot Antivirus
scanning engine for primary scan but has in addition to that a system of
system of internal heuristics devised to search for unknown viruses.

Please note that the license explicitly permits that F-Prot Antivirus BSD
Mail Servers be used for evaluation purposes only, without charge for a
period of no more than 60 days.  If you use this software after the 60 day
evaluation period, then you must register and pay a license fee.

WWW: http://www.f-prot.com/