Postfix and Mailman deliver enhanced e-mail security and performance, Feb 8 2008
Postfix isn't Sendmail's only challenger. Zmailer, Smail, qmail, Post.Office, exim, the Sun Internet Mail Server (SIMS), MMDF, CommuniGate, PMDF, Netscape Messaging Server, and a variety of other products offer specific benefits for Unix-hosted e-mail service. Postfix is the newest of these, however, and worth a look.
Postfix Connection Cache, Feb 8 2008
The Postfix connection cache is shared among Postfix mail delivering processes. This maximizes the opportunity to reuse an open connection. Other MTAs such as Sendmail or exim have a non-shared connection cache. Here, a connection can be reused only by the mail delivering process that creates the connection. To get the same performance improvement as with a shared connection cache, non-shared connections need to be kept open for a longer time.