Scanners

You can choose Qmail-scanner or simscan for email scanning.
Simscan

Simscan is a simple program that enables the qmail smtpd service to reject viruses, spam, and block attachments during the SMTP conversation so the processing load on the email system is kept to a minimum You can find more information about Simscan here.

QMail-Scanner

Qmail-Scanner is an e-mail content scanner that enables a qmail server to scan all messages it receives for certain characteristics (normally viruses), and react accordingly. For more information see http://qmail-scanner.sourceforge.net