SUSE's MTA of choice is Postfix. Postfix was designed by Witse Venema, who at the time had an internship at IBM, with the idea to build from the ground up a secure and scalable MTA. The most popular MTA, sendmail, is often considered difficult to get to grips with because the configuration format is obscure.
Postfix's reliability and security features, as well as having a much simpler parameter=value configuration format has helped it balloon to an extremely popular MTA.
Postfix is constantly being maintained by Venema and other developers, with bug fixes and feature releases released on a constant basis.
Note In general, the speed at which bugs and security updates are released is astonishing —not just for Postfix, but also for the kernel and other high-traffic software releases. The last thing you need when relying on a piece of software is to not have the backup from the developers to fix security issues (although this is a rare occurrence in the Linux world compared to "some" operating systems) or implement new features.
When installed, by default, Postfix is configured to accept mail locally for users existing in your machine's domain. Postfix's default security settings also stop your machine from acting as an open relay.
Note An open relay is a mail server that allows any user to send mail through your mail server, regardless of their location (in your local network or the Internet). This has proven to be a large contributor to the existence of spam as malicious users can use your mail server to send large quantities of mail on the back of your network bandwidth.
The "out of the box" security features of Postfix have contributed to its success, and these security features can be extended even further by adding granularity for UCE (unsolicited commercial email) and user authentication for relay controls.
Postfix is commonly configured in three main ways to provide MTA services to your organization, and we discuss these throughout the chapter:
♦ Always-on, Internet facing mail server.
♦ Dial-up/laptop mail server mainly used for sending mail from your machine only.
♦ Local mail delivery only. This is used to mainly route mail messages that originate from your local machine and is the default for a SUSE installation.
Local mail delivery is also capable of connecting to other Simple Mail Transport Protocol (SMTP) servers if mail is sent using the Postfix mail system, and we discuss this later in the chapter.
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