Over the years, sendmail has grown to be enormously complex. Its complexity makes it challenging to configure if you want to set up something more than a simple mail server. Its size and complexity also add to its vulnerability. For optimal security, make sure you run the latest version of sendmail and always keep sendmail up-to-date. You might consider using one of the following alternatives.
Postfix (postfix package) is an alternative MTA. Postfix attempts to be fast and easy to administer, while also being sendmail compatible enough to not upset sendmail users. Postfix has a good reputation for ease of use and security and is a drop-in replacement for sendmail. Documentation for Postfix can be found at www.postfix.org/docs.html.
Qmail is a direct competitor of Postfix and has the same objectives. By default, Qmail stores email using the maildir format as opposed to the mbox format that other MTAs use (page 632). The Qmail Web site is www.qmail.org.