Postfix logs all failed and successful deliveries to a logfile. The file is usually called /var/log/maillog or /var/log/mail; the exact pathname is defined in the /etc/syslog.conf file.

When Postfix does not receive or deliver mail, the first order of business is to look for errors that prevent Postfix from working properly:

% egrep '(warning|error|fatal|panic):' /some/log/file | more

Note: the most important message is near the BEGINNING of the output. Error messages that come later are less useful.

The nature of each problem is indicated as follows:

• “panic” indicates a problem in the software itself that only a programmer can fix. Postfix cannot proceed until this is fixed.
• “fatal” is the result of missing files, incorrect permissions, incorrect configuration file settings that you can fix. Postfix cannot proceed until this is fixed.
• “error” reports an error condition. For safety reasons, a Postfix process will terminate when more than 13 of these happen.
• “warning” indicates a non-fatal error. These are problems that you may not be able to fix (such as a broken DNS server elsewhere on the network) but may also indicate local configuration errors that could become a problem later.