Email remains the killer information and communications technology. Email volume shows no sign of diminishing, despite the increasing popularity of collaborative messaging tools. There were over 330 billion emails sent in 2021.
Messages are exchanged between hosts using the Simple Mail Transfer Protocol with software programs called mail transfer agents, and delivered to a mail store by programs called mail delivery agents, frequently referred to as email clients.
Within the Internet email system, a message transfer agent, or mail transfer agent, or mail relay is software that transfers electronic mail messages from one computer to another using SMTP. The terms mail server, mail exchanger, and MX host are also used in some contexts.
Here’s our verdict on email servers for Linux. All of the servers are published under an open source licence.
Let’s explore the 12 email servers. For each title we have compiled its own portal page, a full description with an in-depth analysis of its features, together with links to relevant resources.
| Email Servers | |
|---|---|
| Exim | Highly configurable mail transfer agent |
| DBMail | Enables storing and retrieving mail messages from a database |
| OpenSMTPD | Implementation of the server-side SMTP protocol with additional extensions |
| Zimbra | Zimbra Collaboration Suite |
| Postfix | Popular mail transfer agent |
| Courier | Integrated mail/groupware server |
| Cyrus IMAP | Email, contacts and calendar server |
| Dovecot | Secure POP3 server that supports mbox and maildir mailboxes |
| Citadel | Exchange-killer groupware server |
| chasquid | SMTP server with a focus on simplicity, security, and ease of operation |
| Sendmail | Mail transfer agent for sophisticated mail configurations |
| qmail | Written as a more secure replacement for the Sendmail program |
 Read our complete collection of recommended free and open source software. Our curated compilation covers all categories of software. The software collection forms part of our series of informative articles for Linux enthusiasts. There are hundreds of in-depth reviews, open source alternatives to proprietary software from large corporations like Google, Microsoft, Apple, Adobe, IBM, Cisco, Oracle, and Autodesk. There are also fun things to try, hardware, free programming books and tutorials, and much more. |
In this list, I miss “Kolab”, which is a true fully Open Source Groupware (no restrictions) and has almost all professional features out of the box.
As you say, Kolab is groupware software. We cover groupware software separately here Best Free Groupware Software. We recommend Kolab as a groupware solution; it came 3rd.
Thanks for the reply. Yes you are absolutely right, however, Citadel and Zimbra are also groupware software, and seeing them in this list I thought of Kolab
That’s true, and that why we limited the number of groupware solutions that offer a good email server.
Opensmtpd is missing in this list. It is the standard smtp implementation on OpenBSD, but it is available on major Linux distros as well. Very lightweight to configure.
Ok
After migration to Debian 12, I replaced my Kolab Groupware with iRedMail (I also tested Modoboa).
iRedMail and Modoboa are both worth mentioning.