Mail Server Software for Linux: Postfix, Exim, Dovecot and All-in-One Suites

Applies to: Debian 13 and AlmaLinux 9 package versions (checked in Docker); Postfix 3.10.13 and Dovecot 2.4.1 installed and tested on Debian 13

A Linux mail server is not one program but a small set of them. You need a mail transfer agent (MTA) that sends and receives mail over SMTP, usually Postfix or Exim; an IMAP/POP3 server so people can read their mail, usually Dovecot; and spam filtering and DKIM signing on top. You can put these together yourself or install an all-in-one suite that does it for you.

The parts and the usual choices

Versions are the ones in the Debian 13 and AlmaLinux 9 repositories in our check.

• Postfix (MTA): 3.10.13 on Debian 13, 3.5.25 on AlmaLinux 9. Virtualmin uses Postfix, and so do the Ucartz guides for sending mail from your own server.
• Exim (MTA): 4.98.2 on Debian 13, 4.99.5 from EPEL on AlmaLinux 9 (it isn’t in the AlmaLinux base repositories). cPanel servers use Exim; WHM has an Exim Configuration Manager.
• Sendmail and OpenSMTPD (MTAs): also packaged in Debian 13 (Sendmail 8.18.1, OpenSMTPD 7.6.0p1) and can replace Postfix or Exim.
• Dovecot (IMAP and POP3): 2.4.1 on Debian 13, 2.3.16 on AlmaLinux 9. Mind the version: according to the Dovecot documentation, 2.3 settings will not work in 2.4 without changes. The Debian 13 dovecot.conf starts with dovecot_config_version = 2.4.0, so guides written for 2.3 need adapting.
• Rspamd 3.12.1 or SpamAssassin 4.0.1 (spam filtering). Rspamd can also sign outgoing mail with DKIM.
• OpenDKIM 2.11.0 beta 2 (DKIM signing for Postfix or Sendmail).
• Roundcube 1.6.18 (webmail in the browser).

A quick look after installing on Debian 13:

$ postconf mail_version
mail_version = 3.10.13
$ dovecot --version
2.4.1-4 (7d8c0e5759)

All-in-one mail server suites

• mailcow: dockerized: runs as a set of Docker containers; its compose file includes Postfix, Dovecot, Rspamd, ClamAV, SOGo (webmail and groupware), MySQL and Nginx. A good fit if you are comfortable with Docker.
• Mail-in-a-Box: according to its README it turns a fresh Ubuntu 22.04 LTS 64-bit machine into a mail server with Postfix, Dovecot, Roundcube, Nextcloud for contacts and calendars, SpamAssassin, and its own DNS server that sets SPF, DKIM and DMARC records. Install it only on a fresh server that does nothing else.
• iRedMail: an installer script. Its README lists Debian 12 and 13, Ubuntu 22.04, 24.04 (recommended) and 26.04, AlmaLinux and Rocky Linux 9 and 10, CentOS Stream 9 and 10, FreeBSD 14 and OpenBSD 7.8.
• Stalwart: one program written in Rust that handles SMTP, IMAP, JMAP, POP3, CalDAV, CardDAV and WebDAV. Dual-licensed under AGPL-3.0 and a commercial licence.

We didn’t install the suites; the details above come from their official repositories.

Which one should you use?

• Only sending from your apps (password resets, notifications): Postfix on its own is enough. See install and configure Postfix for sending.
• Mailboxes for a few domains with little upkeep: a suite such as mailcow or Mail-in-a-Box on a server of its own.
• Websites and mail on one server: a control panel. cPanel (Exim) and Virtualmin (Postfix) set up mail, DNS and webmail for each domain.
• Full control: Postfix, Dovecot and Rspamd put together by hand. Most flexible, and most work.

Before you install anything

1. Outgoing port 25 must be open, or your server can’t deliver mail to other mail servers. All Ucartz servers have port 25 open; you can check that outgoing port 25 works.
2. A proper host name and reverse DNS: the server name (for example mail.example.com) should resolve to the IP, and the IP’s PTR record back to the name. See set reverse DNS.
3. SPF, DKIM and DMARC records for every domain you send from: SPF, DKIM with OpenDKIM and DMARC.
4. Backups and monitoring: mail is hard to recover once lost, and a full disk stops delivery.

If you would rather have a server built for mail, see email server hosting.

Official documentation: Postfix documentation, mailcow, Mail-in-a-Box, iRedMail and Stalwart.