postfix-master/goals.html

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   5 <title>Postfix Overview - Goals and Features</title>
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  12 <h1><a href="big-picture.html"><img src="small-picture.gif" width="115" height="45"></a> Postfix
  13 Overview - Goals and Features</h1>
  14
  15 <hr>
  16
  17 <p> <strong> Note: this web page is no longer maintained. It exists
  18 only to avoid breaking links in web pages that describe earlier
  19 versions of the Postfix mail system. </strong> </p>
  20
  21 <a href="docs.html">Up one level</a> | <a
  22 href="motivation.html">Introduction</a> | Goals and features | <a
  23 href="architecture.html">Global architecture</a> | <a
  24 href="queuing.html">Queue Management</a> | <a
  25 href="security.html">Security</a>
  26
  27 <h2>Primary goals</h2>
  28
  29 The goal of the Postfix project is to implement a viable alternative
  30 to the UNIX Sendmail program.  Specific goals, and the ways that
  31 Postfix attempts to achieve them are:
  32
  33 <ul>
  34
  35 <li>Wide dissemination. Postfix must be adopted by lots of people
  36 in order to make a significant impact on Internet mail performance
  37 and security. Therefore the software is given away for free, with
  38 no strings attached to it.
  39
  40 <p>
  41
  42 <li>Performance. Postfix is up to three times as fast as its nearest
  43 competitor.  A desktop PC running Postfix can receive and deliver
  44 a million <i>different</i> messages per day. Postfix uses web server
  45 tricks to reduce process creation overhead and uses other tricks
  46 to reduce file system overhead, without compromising reliability.
  47
  48 <p>
  49
  50 <li>Compatibility. Postfix is designed to be sendmail-compatible
  51 to make migration easy.  Postfix supports <b>/var[/spool]/mail</b>,
  52 <b>/etc/aliases</b>, <b>NIS</b>, and <b>~/.forward</b> files.
  53 However, Postfix also attempts to be easy to administer, and
  54 therefore it does <i>not</i> use <b>sendmail.cf</b>.
  55
  56 <p>
  57
  58 <li>Safety and robustness.  Postfix is designed to behave rationally
  59 under stress.  When the local system runs out of disk space or
  60 memory, the Postfix software backs off, instead of making the
  61 problem worse. By design, no Postfix program keeps growing as the
  62 number of messages etc. increases. Postfix is designed to stay in
  63 control.
  64
  65 <p>
  66
  67 <li>Flexibility. Postfix is built from over a dozen little programs
  68 that each perform only one specific task: receive a message via
  69 SMTP, deliver a message via SMTP, deliver a message locally, rewrite
  70 an address, and so on.  Sites with specific requirements can replace
  71 one or more little programs by alternative versions. And it is easy
  72 to disable functionality, too: firewalls and client workstations
  73 don't need local delivery at all.
  74
  75 <p>
  76
  77 <li>Security. Postfix uses multiple layers of defense to protect
  78 the local system against intruders. Almost every Postfix daemon
  79 can run in a <i>chroot</i> jail with fixed low privileges. There
  80 is no direct path from the network to the security-sensitive local
  81 delivery programs - an intruder has to break through several other
  82 programs first. Postfix does not even trust the contents of its
  83 own queue files, or the contents of its own IPC messages. Postfix
  84 filters sender-provided information before exporting it via
  85 environment variables.  Last but not least, no Postfix program is
  86 <i>set-uid</i>.
  87
  88 </ul>
  89
  90 <h2>Other significant features of interest</h2>
  91
  92 <ul>
  93
  94 <li><a href="rewrite.html#transport">Multiple transports</a>.  In
  95 the past the author has configured Sendmail systems that could
  96 relay between Internet, DECnet, X.400 and UUCP.  Postfix is designed
  97 to be flexible enough that it can operate in such environments
  98 without requiring virtual domain or alias kludges.  However, the
  99 initial release only talks SMTP, and has only limited support for
 100 UUCP.
 101
 102 <p>
 103
 104 <li><a href="rewrite.html#virtual">Virtual domains</a>. In the most
 105 common case, adding support for a virtual domain requires change
 106 to only a single Postfix lookup table.  Other mailers usually need
 107 multiple levels of aliasing or redirection to achieve the same
 108 result.
 109
 110 <p>
 111
 112 <li><a href="uce.html">UCE control</a>. Postfix can restrict what
 113 hosts can relay their mail through a Postfix system, and supports
 114 restrictions on what mail is allowed to come in.  Postfix implements
 115 the usual suspects:  blacklists, RBL lookups, HELO/sender DNS
 116 lookups.  Content filtering hasn't been implemented yet.
 117
 118 <p>
 119
 120 <li><a href="rewrite.html">Table lookups</a>. Postfix does not yet
 121 implement an address rewriting language. Instead it makes extensive
 122 use of table lookups. Tables can be local <b>dbm</b> or <b>db</b>
 123 files, or networked <b>NIS</b> or <b>NetInfo</b> maps. Adding
 124 support for other lookup mechanisms is relatively easy.
 125
 126 </ul>
 127
 128 <hr>
 129
 130 <a href="docs.html">Up one level</a> | <a
 131 href="motivation.html">Introduction</a> | Goals and features | <a
 132 href="architecture.html">Global architecture</a> | <a
 133 href="queuing.html">Queue Management</a> | <a
 134 href="security.html">Security</a>
 135
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