This is mailfront, a package containing customizeable network front-ends
for mail servers.  It contains complete SMTP and POP3 front-ends as well
as an authentication module for IMAP.

Two SMTP back-ends are provided.  One delivers mail to qmail-queue,
mimicking most of the behavior of qmail-smtpd, with the addition of
support for SMTP AUTH.  The other rejects all SMTP commands if
$SMTPREJECT is set, and execs its command line otherwise (in order to
run the above program).

WWW: http://untroubled.org/mailfront/