Postfix was originally developed as an alternative to the widely-used Unix SMTP program called Sendmail. It has since become arguably the most powerful SMTP server on the planet. The software is developed and maintained by Wietse Venema, who, along with the open source community, continues to build tremendous functionality and performance enhancements into the software.
Dovecot is an open source IMAP and POP3 server for Linux/UNIX-like systems, written with security primarily in mind. It uses several coding techniques to avoid most of the common performance and security pitfalls. It is fast, secure, and flexible, and has a rich feature set. It is compatible with Exchange, Sendmail, Postfix, Exim, QMail, and other mail transfer agents. Dovecot has a strong support community and is progressing at a rapid pace. KD Interactive Hosted Email has funded the development of several Dovecot features for the open-source community and maintains a small set of custom patches that optimizes performance in our environment.