What is is: [excerpt taken from tls patch]

Frederik Vermeulen <jos-tls@kotnet.org> 20000823
http://www.esat.kuleuven.ac.be/~vermeule/qmail/tls.patch

This patch implements RFC2487 in qmail. This means you can
get SSL or TLS encrypted and authenticated SMTP between
the MTAs and between MTA and an MUA like Netscape4.5 TM.
The code is considered experimental.

WWW: http://www.qmail.org/