Postfix is a free and open source mail transfer agent (MTA), a computer program for the routing and delivery of email. It is intended as a fast, easy-to-administer, and secure alternative to the widely-used Sendmail MTA. Postfix is the default MTA for a number of Unix(-like) operating systems such as Ubuntu.
It is released under the IBM Public License 1.0 which is a free software licence.
Formerly known as VMailer and IBM Secure Mailer, it was originally written by Wietse Venema during a stay at the IBM Thomas J. Watson Research Center, and continues to be actively developed today. Postfix was first released in mid-1999.
Scalix does a fine job using Linux clustering and failover features for maximum uptime. Scalix's AJAX console makes administration a snap, while the included Scalix ActiveSync lets wireless devices connect directly to the server for push e-mail, contact, and calendar updates.