[ Thanks to Jane Walker for this link.
]
“Qpsmtpd is a Perl-based smtpd daemon that was developed by Ask
Bjørn Hansen. Qpsmtpd is used for spam protection on
apache.org, cpan.org and perl.org, and a number of others. It
provides all the standard SMTP functionality and is supported by a
series of extensible plug-ins, also written in Perl.“In this two-part tip, I will demonstrate how to use qpsmtpd. In
the first part, I will show you how to install qpsmtpd. The tip
assumes you are using a Linux-based distribution such as Red Hat
Enterprise Linux. In the second half, I’ll demonstrate how to
configure qpsmtpd and put it in front of your existing MTA…”