Starting Postfix the First Time
There are two important issues to deal with before starting Postfix for the first time. The first is how your system identifies itself. Postfix uses a configuration parameter called myhostname, which must be set to the fully qualified hostname of the system Postfix is running on. Once Postfix knows the fully qualified hostname, it can use that hostname to set default values for other important parameters, such as mydomain. If the parameter myhostname is not set, Postfix defaults to the hostname reported by the system itself. There is a complete discussion of myhostname later in the chapter. You can see what name your system reports with the Unix hostname command:
$ hostname mail.example.com
A fully qualified hostname is comprised of both the individual hostname and the domain in which it resides. Some systems are configured with their simple hostname, rather than its fully qualified version:
$ hostname mail
If your system is configured with just its simple hostname, Postfix cannot determine what the fully qualified name is. You must therefore explicitly set the myhostname parameter. You can do this quite easily with the postconf Postfix command. The postconf command is a Postfix utility that provides an easy way to get a variety of information about your Postfix system. One of its functions is to display or change a specific configuration parameter. You can use it to set the myhostname parameter:
# postconf -e myhostname=mail.example.com
The -e option tells postconf to edit the configuration with the parameters and values specified. If your system is configured with its fully qualified hostname, you don't have to do anything to the Postfix configuration.
The second important issue before starting Postfix for the first time is to make sure that your system's aliases database is in the correct format. There are certain required aliases that you should configure when operating your mail server in a production environment. We'll discuss the aliases file later in this chapter. For now, be aware that it is a text file that must be mapped into an indexed, binary format. Your existing aliases binary format might be different from what Postfix uses by default on your system. You can rebuild the indexed file with the newaliases command:
# newaliases
This command doesn't require any arguments, and it simply recreates your alias database without making any changes to your actual alias file.
Having accomplished these two critical items, you are now ready to start Postfix. Execute the following command:
# postfix start
If Postfix encounters any problems at start up, it reports them to your terminal. After some initial setup, Postfix detaches from the terminal and can no longer report problems to the screen. It will, however, continue to send a lot of information to your system log. Whenever you start or reload Postfix, be sure to check your system's log to make sure that there are no reported errors or warnings. See Section 4.4.1 later in this chapter for information on Postfix logging and how to find the log file it uses.
Under most circumstances, Postfix will start without any problems, and you should now be the proud administrator of a currently running, fully functional Postfix system. See Chapter 7 for information about configuring Postfix to work with a POP/IMAP server, so that your users do not need shell access to your mail system. You should also review Chapter 6 for important information on DNS and email.
To read about stopping and restarting Postfix, see Section 4.4.2 later in this chapter. The rest of this chapter discusses Postfix configuration and administration.