Exim vs Postfix: A Comparison

In this day and age, it is not possible to imagine any business environment without email messages. One aspect of setting up an email server for your company that is often overlooked is the selection of your mail transfer agent (MTA). MTA is also an abbreviation for mail transport agent or message transfer agent. No matter what you call it, an MTA plays an important role in everyday mail communication. An MTA is software that is responsible for transferring your electronic mail messages to the correct mail server, which an MTA finds by querying the MX records of the recipient.

When choosing your MTA, there are a few things to consider:

• Performance.
• Configurability.
• Security policy.
• The transparency of the infrastructure.

Two of the most used mail transfer agents are Exim and Postfix. Both are email server software for Linux that are responsible for transferring your mail across the network. This article will list the advantages and disadvantages of Exim vs Postfix MTAs to discover which one is best for your needs.

What is Exim?

Exim is one of the most used email server software for Unix-like operating systems, such as Linux, Solaris, and more. It was developed at the University of Cambridge as free software under the GNU General Public License terms, which means that Exim is an open source MTA. The user has the freedom to use it, study the code, and modify it. 

So what makes it stand out when comparing Exim vs Postfix?

Advantages of Exim

As Exim is one of the open source mail servers, it is consequently among the best mail transfer agents in regard to its customization and configuration abilities. It is currently used as a default MTA on Debian-based Linux systems, including Ubuntu. 

Variables in Exim

One of the more handy features is declaring variables. The values for those variables can be taken from the incoming email messages and manipulated further.

For example, those variables can be used to further filter the receiving email messages. Exim also has its own scripting language that provides you with the ability to write custom scripts for email processing.

Exim Logs

Users also love Exim because of its logging abilities. It writes three different logs used to prevent email spamming. The logs are the main log, the panic log, and the reject log.

Troubleshooting Issues with Exim 

Exim has a large online community that actively shares information which is extremely useful when troubleshooting issues and finding bug fixes. There is also a large amount of documentation available online, so when a user encounters any issues, he or she is likely to find a solution with a few clicks and a bit of reading.

Customization 

Exim is compatible with Sendmail and is proven to be an excellent mail transfer agent if the user needs to customize its mail configuration. In order to customize your Exim configuration, you can simply use the Exim Configuration Manager interface within the Service Manager in WHM, or you can customize the exim.conf file.

Disadvantages of Exim

Complexity 

Although its high configurability is considered an advantage, for some users it can be too complex, and that complexity can be considered a disadvantage of sorts. The online community that is offering support is probably a result of Exim’s complexity; it is more difficult to maintain or administer post-deployment.

Queue Processing Performance

Exim is used for a large number of high-traffic web applications because it is efficient in handling massive amounts of emails per hour. Unfortunately, those emails create queues that can have a negative impact on the server’s queue processing performance.

What is Postfix?

Postfix is a free and open source MTA that provides flexibility in administration. It was developed as an alternative to and compatible with the well-known mail transfer agent, Sendmail. In addition, Postfix has a modular architecture composed of several smaller independent executables, contributing to it being secure and fast.

Advantages of Postfix

Postfix and Security

One of the biggest advantages of the Postfix mail transfer agent is definitely security. It was developed by Wietse Zweitze Venema, who is a well known specialist for freeware security. Postfix applies excellent built-in mechanisms against spam bots and malware.

Filtering Options for Postfix

Postfix allows the administrator to use additional software in order to add another layer of filtering. It can reject emails before the incoming SMTP mail transfer is completed thanks to its before-queue content filter.

Major features that are making Postfix one of the most used mail transfer agents are:

• Junk mail control.
• Database support.
• Mailbox support.
• Address manipulation support.

Fast and Easy

Postfix is also known to be fast in performance and easy to configure, as the parameters are specified in the configuration file.

Disadvantages of Postfix

Increase in CPU Usage

While Postfix can have features that use before-content filtering, it can cause some issues on high-traffic servers. As the system load increases, the CPU usage also increases, and eventually, the system has to either stop the before-content filtering, or it has to stop accepting mail.

Memory Issues

Another issue that occurs when using content filtering is that it can use a lot of the server's memory resources. If there is a higher number of simultaneous content filter processes, it can tie up too much of the server's RAM, which can cause issues.

Use Cases for Exim

Given that Exim is probably the most flexible mail transfer agent when it comes to configuration, if you are looking for an MTA that you can configure and customize as you like, Exim would be the better choice.

It has its own scripting language that can be used to write scripts for custom email processing. That way, system administrators can customize Exim the way they see fit.

One more advantage when it comes to Exim is that it comes preconfigured with cPanel. System administrators don’t need to configure it manually.

Use Cases for Postfix

Postfix mail transfer agent would be easier to set up for beginner administrators and it can provide many mail filters out-of-the-box. Postfix can also reject emails before the incoming mail transfer completes. This before-queue content filter can vastly improve your mail server’s security. If you are looking for a more secure option, Postfix is a good choice to use. 

Exim vs Postfix - Who Wins? 

In conclusion, when choosing an MTA, there are a couple of things to take into consideration, such as security, performance, reliability, and configurability. The comparison chart below provides a brief comparison of these two mail transfer agents.

So, which one wins in this Exim vs Postfix clash? It all depends on what you prefer. If security is a big concern of yours, go with Postfix. But if the configurability is more important to you, then Exim is of most benefit to you.

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