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=utf-8"> 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 "$name" and "${name}" are recursively 46replaced with the value of the named parameter. The parameter name 47must contain only characters from the set [a-zA-Z0-9_]. 48An undefined parameter value is replaced with the empty value. </p> 49 50<li> <p> The expressions "${name?value}" and "${name?{value}}" are 51replaced with "value" when "$name" is non-empty. The parameter name 52must contain only characters from the set [a-zA-Z0-9_]. These forms are 53supported with Postfix versions ≥ 2.2 and ≥ 3.0, respectively. 54</p> 55 56<li> <p> The expressions "${name:value}" and "${name:{value}}" are 57replaced with "value" when "$name" is empty. The parameter name must 58contain only characters from the set [a-zA-Z0-9_]. These forms are 59supported with Postfix versions ≥ 2.2 and ≥ 3.0, respectively. 60</p> 61 62<li> <p> The expression "${name?{value1}:{value2}}" is replaced 63with "value1" when "$name" is non-empty, and with "value2" when 64"$name" is empty. The "{}" is required for "value1", optional for 65"value2". The parameter name must contain only characters from the 66set [a-zA-Z0-9_]. This form is supported with Postfix versions 67≥ 3.0. </p> 68 69<li> <p> The first item inside "${...}" may be a relational expression 70of the form: "{value3} == {value4}". Besides the "==" (equality) 71operator Postfix supports "!=" (inequality), "<", "≤", "≥", 72and ">". The comparison is numerical when both operands are all 73digits, otherwise the comparison is lexicographical. These forms 74are supported with Postfix versions ≥ 3.0. </p> 75 76<li> <p> Each "value" is subject to recursive named parameter and 77relational expression evaluation, except where noted. </p> 78 79<li> <p> Whitespace before or after each "{value}" is ignored. </p> 80 81<li> <p> Specify "$$" to produce a single "$" character. </p> 82 83<li> <p> The legacy form "$(...)" is equivalent to the preferred 84form "${...}". </p> 85 86</ul> 87 88<li> <p> When the same parameter is defined multiple times, only 89the last instance is remembered. </p> 90 91<li> <p> Otherwise, the order of main.cf parameter definitions does 92not matter. </p> 93 94</ul> 95 96<p> The remainder of this document is a description of all Postfix 97configuration parameters. Default values are shown after the 98parameter name in parentheses, and can be looked up with the 99"<b>postconf -d</b>" command. </p> 100 101<p> Note: this is not an invitation to make changes to Postfix 102configuration parameters. Unnecessary changes are likely to impair 103the operation of the mail system. </p> 104 105<dl> 106
