P3Scan is a transparent POP3-Proxy with virus-scanning capabilities.
This means that all your POP3-Clients in the Network can't fetch mails
from the internet without that P3Scan have scanned it. If a virus has
been found the mail is replaced with a notification and the original
(infeceted) version is stored on the harddisc. Transparent means, that
neither the client nor any of the used POP3-servers has to be configured. 

This port is based on mail/pop3vscan, but the development for that
port seems to have ceased.

WWW: http://p3scan.sourceforge.net/