Qexplore
Qexplore enables a Qmail server to analyze emails.
... SQLite (http://www.sqlite.org).
Unlike other scanners for Qmail, such as Simscan or Qmail-Scanner which are inline scanners, Qexplore is an offline scanner that first write an email to a queue resident on disk, closing the qmail-smtpd communication.
It than (offline) analyzes this email to check for virus and/or spam. This design solves the problem of highly traffic smtp servers in wich a lot of concurrent SMTP connections can deny access of incoming/outgoing emails because the system is busy.