Linux Consultant

Linux Mail Server Software- A Comparison of Popular Mail Transfer Agents

With the growing popularity of Linux server solutions, many clients often ask me, “What is the best mail server software for my needs?”. A Mail Transfer Agent, or MTA, is a software package that allows your Linux server to send and receive mail. There are many different MTAs out there, and each MTA has it's own specific strengths and weaknesses. This article will cover the more popular MTAs- Exim, Postfix, Sendmail, Qmail, and Zimbra. Although Zimbra is more of a productivity suite than a MTA, it is worth mentioning due to it's extensive features.


Exim


Exim has been out since 1995, and growing in popularity ever since. The biggest strength of Exim is it's almost infinite level of customization. Exim supports the ability for a server administrator to create a custom ruleset that handles incoming and outgoing emails in any particular manner. For instance, it is easier with Exim to create a custom rule that routes incoming mail from a particular domain past anti-virus and anti-spam filters. One disadvantage is that Exim has had a less than stellar history with security. Exim3 was vulnerable to numerous security vulnerabilities, but it appears so far that Exim4 is more secure. Although Exim was not designed for performance, Exim can be configured to run as a high performance mail server. Exim is an excellent MTA if you need to create a complex or custom mail configuration. Exim is the default MTA on Debian Linux.


Postfix


Postfix is possibly the fastest growing MTA on the market today. Postfix is extremely popular because of it's performance, and it's past security history. It is far harder (or almost impossible) to compromise the root user on a server that runs Postfix, than for instance Sendmail or Exim. Postfix also supports the use of milters, which allow you to use external software solutions to pass mail from Postfix to anti-virus and anti-spam filters. Postfix also runs faster with less system resources than most other MTAs (or at least, with standard configurations). Standard configurations are easy to create, but if you need a unique setup, it can be a pain with Postfix. These strengths leave little mystery as to the sudden growth of Postfix as a Linux mail server software solution. Postfix is the default MTA on Ubuntu Linux.


Sendmail


Sendmail is the most popular Linux mail server software solution. Written in 1982, Sendmail is literally the standard by which all other MTAs are compared. Sendmail has lost most of it's popularity in recent years though, due to security issues, and a difficult configuration. Sendmail is the most difficult MTA to configure, and has had more than it's fair share of security vulnerabilities and compromises. The few administrators that run Sendmail either do so for compatibility reasons (it was, after all, the classic UNIX mail server), or for comfortability (UNIX admins will sometimes cling to Sendmail, because they are used to it's over complicated configuration). Red Hat Enterprise Linux uses Sendmail by default.


Qmail


Qmail is the one of the most secure Linux mail server software solutions on the market today. Although unsupported, and not currently in development (Qmail hasn't been updated since 1997), Qmail has a large fan base. Qmail is also faster, and scales better with higher mail loads than Sendmail. However, Qmail is not easy to configure, or easy to extend. Qmail does not support Sendmail milters, so any additional filters have to be specifically written for Qmail. Qmail is the default MTA in the popular Plesk control panel software.


Zimbra


Zimbra is the least popular of all the Linux mail server software mentioned. Zimbra is not designed for security, speed, or infinite customization- it is designed for group collaboration. Zimbra is extremely easy to install and configure, but should not be used as a high performance MTA. Zimbra instead excels if you want to have a way to share calendars, files, and contacts with other users on the Zimbra mail server. A web-based control panel allows an easy way to add or remove users from the mail server, and most configuration is just as easy. Zimbra offers a commercial version, as well as an open source version of it's mail server. Currently, no Linux distributions use Zimbra as the default mail server.


The Best Linux Mail Server Software


The best Linux mail server software for your needs can be either MTA mentioned in this article- it's all up to your needs. For most organizations and people, Sendmail fills that role very well. If you don't need enterprise features, or the best security record, Sendmail clearly stands out based on it's performance and features. Exim is a close second, followed by Qmail, Zimbra, and Sendmail (in that order of preference). Qmail's excellent security record is it's biggest strength, and Sendmail's popularity is quickly vanishing. In the end, the best Linux mail server software for your server depends on your needs- and your needs alone. If you have any further questions about which mail server software would be best for your needs, feel free to contact me.