                 Postfix Overview - Goals and Features
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   The goal of the Postfix project is to implement a viable alternative
   to the UNIX Sendmail program. Specific goals, and the ways that
   Postfix attempts to achieve them are:

     * Wide dissemination. Postfix must be adopted by lots of people in
       order to make a significant impact on Internet mail performance
       and security. Therefore the software is given away for free, with
       no strings attached to it.

     * Performance. Postfix is up to three times as fast as its nearest
       competitor. A desktop PC running Postfix can receive and deliver a
       million different messages per day. Postfix uses web server tricks
       to reduce process creation overhead and uses other tricks to
       reduce file system overhead, without compromising reliability.

     * Compatibility. Postfix is designed to be sendmail-compatible to
       make migration easy. Postfix supports /var/mail,
       /etc/aliases, NIS, and ~/.forward files. However, Postfix also
       attempts to be easy to administer, and therefore it does not use
       sendmail.cf.

     * Safety and robustness. Postfix is designed to behave rationally
       under stress. When the local system runs out of disk space or
       memory, the Postfix software backs off, instead of making the
       problem worse. By design, no Postfix program keeps growing as the
       number of messages etc. increases. Postfix is designed to stay in
       control.

     * Flexibility. Postfix is built from over a dozen little programs
       that each perform only one specific task: receive a message via
       SMTP, deliver a message via SMTP, deliver a message locally,
       rewrite an address, and so on. Sites with specific requirements
       can replace one or more little programs by alternative versions.
       And it is easy to disable functionality, too: firewalls and client
       workstations don't need local delivery at all.

     * Security. Postfix uses multiple layers of defense to protect the
       local system against intruders. Almost every Postfix daemon can
       run in a chroot jail with fixed low privileges. There is no direct
       path from the network to the security-sensitive local delivery
       programs - an intruder has to break through several other programs
       first. Postfix does not even trust the contents of its own queue
       files, or the contents of its own IPC messages. Postfix avoids
       placing sender-provided information into shell environment
       variables. Last but not least, no Postfix program is set-uid.
       
Other significant features of interest

     * Multiple transports. In the past the author has configured
       Sendmail systems that could relay between Internet, DECnet, X.400
       and UUCP. Postfix is designed to be flexible enough that it can
       operate in such environments without requiring virtual domain or
       alias kludges. However, the initial release only talks SMTP, and
       has only limited support for UUCP.

     * Virtual domains. In the most common case, adding support for a
       virtual domain requires change to only a single Postfix lookup
       table. Other mailers usually need multiple levels of aliasing or
       redirection to achieve the same result.

     * UCE control. Postfix can restrict what hosts can relay their
       mail through a Postfix system, and supports restrictions on what
       mail is allowed to come in. Postfix implements the usual suspects:
       blacklists, RBL lookups, HELO/sender DNS lookups. Content
       filtering hasn't been implemented yet.

     * Table lookups. Postfix does not yet implement an address
       rewriting language. Instead it makes extensive use of table
       lookups. Tables can be local dbm or db files, or networked NIS or
       NetInfo maps. Adding support for other lookup mechanisms is
       relatively easy.
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WWW: http://www.postfix.org/
