qpsmtpd is actively developed, but very stable software. We typically make a new release every 3-9 months.
Latest release: 0.84 (April 7, 2010)
Previous release: 0.83 (September 15, 2009)
See the Change log
You can also get qpsmtpd with Git.
Many users are using custom `forks` with their particular value-added changes on top. If you go that route it's highly recommended that you fork from git to make it easier to contribute back the changes you wish to share.
git clone git://git.develooper.com/qpsmtpd.git or git clone git://github.com/smtpd/qpsmtpd.git
You can browse the repository (also on github).
qpsmtpd has been used for the primary perl.org mail servers since 2001. At apache.org they are also using qpsmtpd for their mail services. Years ago a happy user wrote and told that qpsmtpd is rejecting several hundred thousand spams a day on his server; these days that's too common to be exceptional.