A Mail server is a computer server which provides SMTP, POP3 and/or IMAP services. This enables the sending and receiving of email messages.
There are several programs that run on mail servers:
- Sendmail - The most versatile, but the one with the most cryptic configuration file. It has had a history of security holes, including the Morris worm.
- Postfix[?] - By Wietse venema[?]. This MTA is designed for security, with several separate programs each of which does a task.
- qmail - By Dan Bernstein. Similar in design to Postfix. Additionally the programs run as different user IDs.
- Exim
- Courier
- UW IMAP - Uses mbox format.
- Courier IMAP - Uses Maildir format, which is much faster and requires no file locking.
- Procmail - A general-purpose mail-sorting program.
- Vipul's Razor - By Vipul Ved Prakash[?]. Razor users (which may be spamtraps) report spam to Razor; mail servers ask Razor whether incoming messages are spam.
- SpamAssassin - Uses several criteria, including Razor, to recognize spam.