1<!doctype html public "-//W3C//DTD HTML 4.01 Transitional//EN" 2 "http://www.w3.org/TR/html4/loose.dtd"> 3 4<html> 5 6<head> 7 8<title>Postfix Configuration Parameters </title> 9 10<meta http-equiv="Content-Type" content="text/html; charset=us-ascii"> 11 12</head> 13 14<body> 15 16<h1><img src="postfix-logo.jpg" width="203" height="98" alt="">Postfix Configuration Parameters </h1> 17 18<hr> 19 20<h2> Postfix main.cf file format </h2> 21 22<p> The Postfix main.cf configuration file specifies a very small 23subset of all the parameters that control the operation of the 24Postfix mail system. Parameters not explicitly specified are left 25at their default values. </p> 26 27<p> The general format of the main.cf file is as follows: </p> 28 29<ul> 30 31<li> <p> Each logical line is in the form "parameter = value". 32Whitespace around the "=" is ignored, as is whitespace at the end 33of a logical line. </p> 34 35<li> <p> Empty lines and whitespace-only lines are ignored, as are 36lines whose first non-whitespace character is a `#'. </p> 37 38<li> <p> A logical line starts with non-whitespace text. A line 39that starts with whitespace continues a logical line. </p> 40 41<li> <p> A parameter value may refer to other parameters. </p> 42 43<ul> 44 45<li> <p> The expressions "$name", "${name}" or "$(name)" are 46recursively replaced by the value of the named parameter. </p> 47 48<li> <p> The expression "${name?value}" expands to "value" when 49"$name" is non-empty. This form is supported with Postfix version 502.2 and later. </p> 51 52<li> <p> The expression "${name:value}" expands to "value" when 53"$name" is empty. This form is supported with Postfix version 2.2 54and later. </p> 55 56<li> <p> Specify "$$" to produce a single "$" character. </p> 57 58</ul> 59 60<li> <p> When the same parameter is defined multiple times, only 61the last instance is remembered. </p> 62 63<li> <p> Otherwise, the order of main.cf parameter definitions does 64not matter. </p> 65 66</ul> 67 68<p> The remainder of this document is a description of all Postfix 69configuration parameters. Default values are shown after the 70parameter name in parentheses, and can be looked up with the 71"<b>postconf -d</b>" command. </p> 72 73<p> Note: this is not an invitation to make changes to Postfix 74configuration parameters. Unnecessary changes are likely to impair 75the operation of the mail system. </p> 76 77<dl> 78