Postfix is a Mail Transport Agent (MTA), supporting LDAP, SMTP AUTH (SASL),
TLS and running in a chroot environment.

Postfix is Wietse Venema's mailer that started life as an alternative
to the widely-used Sendmail program.
Postfix attempts to be fast, easy to administer, and secure, while at
the same time being sendmail compatible enough to not upset existing
users. Thus, the outside has a sendmail-ish flavor, but the inside is
completely different.
This software was formerly known as VMailer. It was released by the end
of 1998 as the IBM Secure Mailer. From then on it has lived on as Postfix.

This rpm supports different build time options, to enable or disable these
features you must rebuild the source rpm using the --with ... or --without ...
rpm option.
Currently postfix has been built with:

Smtpd multiline greeting: --without multiline
Virtual Delivery Agent: --without VDA
Munge bare CR: --without barecr
TLS support: --with tls
IPV6 support: --with ipv6
CDB support: --with cdb
Chroot by default: --with chroot