Postfix Configuration - Basics

Introduction

Postfix has about 100 configuration parameters that are controlled via the main.cf file. Fortunately, they have sensible default values. In most cases, you need to configure only two or three parameters before you can use the Postfix mail system:

What domain to use in outbound mail
What domains to receive mail for

The default values for many other configuration parameters are derived from just these two.

The third parameter of interest controls the amount of mail sent to the local postmaster:

What trouble to report to the postmaster

By the way, if you change parameters of a running Postfix system, don't forget to issue a postfix reload command.

If you run Postfix on a virtual network interface, or if your machine runs other mailers on virtual interfaces, you'll have to look at the other parameters listed here as well:

My own hostname
My own domain name
My own networks
My own network addresses

What domain to use in outbound mail

The myorigin parameter specifies the domain that appears in mail that is posted on this machine. The default is to use the local machine name, $myhostname, which defaults to the name of the machine. Unless you are running a really small site, you probably want to change that into $mydomain, which defaults to the parent domain of the machine name.

Examples:: myorigin = $myhostname (default); myorigin = $mydomain (probably desirable)

What domains to receive mail for

The mydestination parameter specifies what domains this machine will deliver locally, instead of forwarding to another machine. The default is to receive mail for the machine itself.

You can specify zero or more domain names, /file/name patterns and/or type:name lookup tables, separated by whitespace and/or commas. A /file/name is replaced by its contents; type:name requests that a table lookup is done, typically from a virtual database.

If your machine is a mail server for its entire domain, you must list $mydomain as well.

Examples:

Default setting:: mydestination = $myhostname localhost.$mydomain
Domain-wide mail server:: mydestination = $myhostname localhost.$mydomain $mydomain
Host with multiple DNS A records:: mydestination = $myhostname localhost.$mydomain www.$mydomain ftp.$mydomain

Caution: in order to avoid mail delivery loops, you must list all hostnames of the machine, including $myhostname, and localhost.$mydomain.

What trouble to report to the postmaster

You should set up a postmaster alias that points to a human person. This alias is required to exist, so that people can report mail delivery problems.

The Postfix system itself also reports problems to the postmaster alias. You may not be interested in all types of trouble reports, so this reporting mechanism is configurable. The default is to report only serious problems (resource, software) to postmaster:

Default:: notify_classes = resource, software
The meaning of the classes is as follows:

bounce
Send postmaster copies of undeliverable mail. If mail is undeliverable, a so-called single bounce message is sent, with a copy of the message that was not delivered. For privacy reasons, the postmaster copy of a single bounce message is truncated after the original message headers. If a single bounce message is undeliverable, the postmaster receives a double bounce message with a copy of the entire single bounce message. See also the luser_relay feature.

2bounce
Send double bounces to the postmaster.

delay
Inform the postmaster of delayed mail. In this case, the postmaster receives message headers only.

policy
Inform the postmaster of client requests that were rejected because of (UCE) policy restrictions. The postmaster receives a transcript of the entire SMTP session.

protocol
Inform the postmaster of protocol errors (client or server side) or attempts by a client to execute unimplemented commands. The postmaster receives a transcript of the entire SMTP session.

resource
Inform the postmaster of mail not delivered due to resource problems (for example, queue file write errors).

software
Inform the postmaster of mail not delivered due to software problems.

My own hostname

The myhostname parameter describes the fully-qualified domain name of the machine running the Postfix system. $myhostname appears as the default value in many other Postfix configuration parameters.

By default, myhostname is set to the local machine name. If your machine name is not in fully-qualified domain name form, or if you run Postfix on a virtual interface, you will have to specify the fully-qualified domain name that the mail system should use.

Examples:: myhostname = host.local.domain (local hostname is not FQDN); myhostname = host.virtual.domain (virtual interface); myhostname = virtual.domain (virtual interface)

My own domain name

The mydomain parameter specifies the parent domain of $myhostname. By default it is derived from $myhostname by stripping off the first part (unless the result would be a top-level domain).

Examples:: mydomain = local.domain; mydomain = virtual.domain (virtual interface)

My own networks

The mynetworks parameter lists all networks that this machine is attached to. This information can be used by the anti-UCE features to distinguish between local systems and strangers.

By default, mynetworks is set to the class A, B or C networks that the machine is attached to. For example, for my machines at home, the result is: 168.100.0.0/16 127.0.0.0/8. However, network 168.100 is owned by my ISP. Of course I do not want to consider all their customer systems as local, so I use instead:

mynetworks = 168.100.189.0/28, 127.0.0.0/8

My own network addresses

The inet_interfaces parameter specifies all network interface addresses that the Postfix system should listen on; mail addressed to user@[network address] will be delivered locally, as if it is addressed to a domain listed in $mydestination.

The default is to listen on all active interfaces. If you run mailers on virtual interfaces, you will have to specify what interfaces to listen on. This includes the non-virtual mailer that receives mail for the machine itself as well: it should never listen on the virtual interfaces or you would have a mailer loop.

Examples:

Default:
inet_interfaces = all

Host running virtual mailers:
inet_interfaces = virtual.host.name (virtual domain)
inet_interfaces = $myhostname localhost.$mydomain (non-virtual mailer)