Appendix A. Configuration Parameters

This appendix contains an alphabetical listing of parameters normally configured in the Postfix main.cf file. The brief descriptions are only meant to give you an idea of the purpose of the parameter. All of the parameters are fully documented in the sample configuration files and manpages that come with the Postfix distribution. This quick reference can point you in the right direction, but you will have to consult the body of this book or the online documentation to understand how each parameter works.

All of the parameters are listed with a type of value that should be assigned to it. Most of the value types are obvious. Those that require some explanation are described here:

Explicit list

The parameter requires one or more items from a specific list of possible values. See the online documentation for a particular parameter to see what the possible values are.

Lookup tables

When a parameter points to lookup tables, the tables are specified with their map type and the table name separated by a colon:

transport_map = hash:/etc/postfix/transport

Pathname

The complete path to a file.

Template

Some parameter values are specified as strings that contain macros:

smtpd_banner = $myhostname ESMTP $mail_name

The macros are expanded into their values at the time the parameter is used. See the online documentation to find out what macros are allowed for a particular template parameter.

Time units

Many parameters are specified as an amount of time:

queue_run_delay = 1000s

They are assigned a value and a time unit abbreviation. Time unit abbreviations are listed in Table A-1. If you leave off the time unit, each time parameter has a default unit that it assumes for the value specified. You can check the online documentation to see what the default unit is for a particular parameter.

Table A-1. Time units

Unit	Abbreviation	Example
Seconds	s	1s
Minutes	m	15m
Hours	h	4h
Days	d	5d
Weeks	w	2w

All of the parameters have a default value (although for some the default is blank). Only parameters that differ from their default values have to be specified in main.cf. The parameters are listed here with their default values, but they sometimes change with Postfix releases. You can check the default value for a parameter with the postconf command and its -d option:

$ postconf -d alias_maps
alias_maps = hash:/etc/aliases, nis:mail.aliases