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By Root 3010 0

the master.cf file that sets limits and controls. The default values set in master.cf are right for all but very slow or very fast machines or networks; in general, no tweaking is necessary. Another configuration file, main.cf, does message routing, rewriting, and filtering. main.cf corresponds loosely to the sendmail.cf file; the master.cf file does not have an analog in sendmail since sendmail consists of a single daemon process.

Several command-line utilities allow users to interact with the mail system:

• postfix – starts and stops the mail system (must be run as root)

• postalias – makes the newaliases command work

• postcat – prints the contents of queue files

• postconf – displays and edits the mail configuration file, main.cf

• postdrop – adds messages to the maildrop queue

• postkick, postlock, postlog – provide locking and logging for shell scripts

• postmap – builds database tables, like the UNIX makemap command

• postsuper – manages the queues (run at startup)

Configuring Postfix

About 100 parameters can be specified in the mail.cf file. Most have sensible defaults. The language looks a bit like a series of Bourne shell assignment statements. In the examples below, we have sometimes annotated the configuration statements with a comment that identifies the sendmail equivalent. These comments at the end of configuration lines are not part of the configuration statements; remove the comments if you want to use the statements in your own configuration.

First, let’s define a few variables that will be used later. The myhostname variable defaults to the machine’s hostname. If it’s not fully qualified, set it manually before using it:

myhostname = host.xxx.yyy

The mydomain variable defaults to the parent domain of $myhostname, which Postfix calculates by stripping off the host portion. If this algorithm won’t give the right result, define the domain yourself:

mydomain = local.domain

Both myhostname and mydomain can specify virtual identities.

The mynetworks variable specifies all the networks to which the machine is connected, including the loopback network. For example:

mynetworks = 128.138.243.64/26, 127.0.0.0/8

Postfix understands CIDR notation for the netmask length. The inet_interfaces variable specifies the interfaces that Postfix should listen on (by default, all active interfaces). You need to specify a value for this variable if you use virtual domains.

For the simplest configuration case, you need configure only three variables:

• myorigin – what domain to use in outgoing mail

• mydestination – what domains to receive mail for

• notify_classes – what types of trouble to report to the postmaster

The variable myorigin determines what domain to use for outgoing mail. Use one of the following:

myorigin = $myhostname

myorigin = $mydomain # like sendmail masquerading

The variable mydestination determines the domains for which we will accept incoming mail; it plays the role of sendmail’s use_cw_file feature. The value assigned to mydestination can be a list of hostnames, a domain, a filename, or a lookup table specification. Here are some examples:

mydestination = $myhostname localhost.$mydomain

mydestination = $myhostname localhost.$mydomain $mydomain

mydestination = /etc/mail/local-host-names

The notify_classes clause determines which problems are brought to the attention of the postmaster. Several classes can result in so much mail that it doesn’t get read. The default is

notify_classes = resource, software

which limits the errors to host machine problems and Postfix software problems. Table 19.21 shows the possible classes.

Table 19.21 Values that can be included in notify_classes

Postfix has options for controlling the resources used by the mail system, both rate controls and resource controls.

Postfix can also do limited address rewriting; for example, it can

• Map login names to first.last style addresses

• Trim source route addresses

• Convert UUCP addresses to domain style

• Undo the %-hack

• Add a