Some Postfix features:
Postfix can send and receive 1 million mails a day.
Postfix was developed to be sendmail compatible in order to ease the migration process. It supports /var/spool/mail, /etc/aliases, NIS and /.forward files. However, for purposes of easing management, it doesn't use the sendmail.cf file.
Postfix was developed to work through stress conditions behaving itself in a "rational" way. It controls memory usage and the amount of sent and received messages this way avoiding server overcharge.
Postfix is built by approximately half a dozen of small programs, each one playing a specific role, e.g.: Send a message via SMTP, send a message locally, receive a message via SMTP, rewrite an address. Its design allows sites with specific requirements to replace one or more of such components by alternative versions that comply with your requests.
Postfix uses multiple security layers to protect local system against attacks. Almost all of the Postfix daemons can run in an environment protected by chroot.