Running Linux, 5th Edition - Matthias Kalle Dalheimer [434]
Postfix has two different release tracks: official and experimental. The experimental releases contain all the latest patches and new features, although these might change before they are included in the official release. Don't be put off by the term "experimental"; these releases are very stable and have been tested thoroughly. If you are looking for a feature that is available only in the experimental release, you should feel more than comfortable using it. Read the release notes for both tracks to know what the current differences are.
A Word About DNS
Before setting up Postfix , you should understand that if your system is going to receive mail from others across the Internet, the DNS for your domain has to be configured correctly. DNS is discussed in Chapter 13.
Let's assume for this discussion that you are configuring a host called halo in the domain example.org and that you have a user account michael on your system. Regardless of how you want to receive mail, your host halo.example.org must have a DNS A record that maps its hostname to its IP address.
In this example your email address is going to be either michael@halo.example.org or michael@example.org. If you want to use the first form, configuring the DNS A record is enough for messages to reach you.
If your system is going to receive all mail for example.org (including michael@example.org), the domain should have a DNS MX record pointing to your host halo.example.org. If you are configuring the DNS for your domain yourself, make sure you read the documentation to understand how it works; otherwise, speak to your DNS administrator or ISP about routing mail to your system.
Postfix frequently uses DNS in its normal operation, and it uses the underlying Linux libraries to perform its DNS queries. Make sure your system is configured correctly to perform DNS lookups (see "Configuring DNS" in Chapter 13). Postfix usually has to find an MX record to make its deliveries. Don't assume that if Postfix reports a DNS problem with an address, and you find that the domain resolves correctly, that email delivery should therefore succeed. If Postfix reports a problem, you can be almost certain there is a problem.
Installing Postfix
Although prepackaged distributions are available, you may want to build the package yourself if you want to use any of the add-on libraries or functions that are not included in your distribution. You might also want to get the latest version to obtain a new feature that has not yet been included in your distribution.
Before you install Postfix, be aware that it includes the three commands /usr/bin/newaliases , /usr/bin/mailq , and /usr/sbin/sendmail that are normally used by sendmail. Postfix provides replacements that work with the Postfix system rather than with sendmail. You should rename your existing sendmail commands so that the Postfix installation doesn't overwrite them in case you ever want to use the original sendmail binaries again:
# mv /usr/bin/newaliases /usr/bin/newaliases.orig
# mv /usr/bin/mailq /usr/bin/mailq.orig
#mv /usr/sbin/sendmail /usr/sbin/sendmail.orig
Postfix uses Unix database files to store its alias and lookup table information. You must, therefore, have the db libraries installed on your system before building Postfix. These libraries are contained within the db-devel RPM package or the Debian libdb4.3-dev package. If you are not using a package manager, you can obtain them directly from Sleepycat Software (http://www.sleepycat.com/). If you are using RPM, execute the following command to see if the necessary libraries have been installed on your system:
# rpm -qa | grep db-devel
db-devel-4.3.27-3
You should see a line similar to the second line in the preceding command that displays the db-devel