Qsmtp is a drop in replacement for the qmail SMTP programs qmail-smtpd
and qmail-remote. That means you just change your startup scripts to use
Qsmtpd instead of qmail-smtpd and most things will work as before.

The initial point was a heavily patched qmail-smtpd to get some decent
antispam features. This was then rewritten from scratch into a new
binary that was designed to allow easy extension to new mail filters.
Another design goal was to be 100% IPv6 clean.

  • Fast and small: written in plain C
  • IPv6 clean
  • Many antispam modules included, e.g. SPF, IP blacklists, domain
    blacklists, badmailfrom, helo filtering
  • Easy API to add your own spamfilters
  • For vpopmail hosts: does not create bounces for non-existing users
  • Tested: includes unit tests, nightly checks available
    at http://my.cdash.org/index.php?project=Qsmtp

This is available at https://opensource.sf-tec.de/Qsmtp/