1. MailCow

MailCow is open-source docker based email server suite. It is a collection of containers linked in one bridged network. Each container represent a single application, such as Dovecot, Memcached, MySQL, PHP, Postfix, Nginx, etc. MailCow provides a web user interface to manage the mail server and email accounts.

MailCow features:

• SOGo web based email

• SMTP and IMAP

• Easy mail client configuration

• Two facto authentication and brute force protection

• Email whitelist/blacklist and spam thresholds

• Process isolation via docker containers

• Web administration

MailCow system requirements: 1GHz CPU, 2GB RAM + Swap, and 5GB storage for the suite.

MailCow (Documentation)

2. Poste.io

Poste.io is open-source docker based mail server that you can setup in 5 minutes. The database is stored in file-based SQLite database. Update, backup, and migration is easy.

Poste.io features:

• Native implementation of SPF, DKIM, DMARC, SRS

• Antivirus engine (ClamAV)

• Spam filter (RSPAMD)

• Email redirection, autoreply, and filters

• Quota limit for mailbox space or email count

• Web administration

• Autodiscovery for email client software

• Server diagnostics

• Process isolation via docker containers

MailCow system requirements: Poste.io does not have a specified system requirements. All you need is a 64-bit Linux distribution, enough CPU and free RAM to run Spamassassin and Clamav, Docker engine running.

Poste.io

3. Mail-in-a-Box

Mail-in-a-Box is an open source software bundle that make it easy to turn a cloud server into your own email server for multiple domains.

Mail-in-a-Box features:

• SMTP and IMAP

• CardDAV/CalDAV through Nextcloud

• Exchange ActiveSync

• Roundcube webmail

• DNS server auto configure SPF, DKIM, DMARC

• Backup to Amazon S3 cloud storage

• Static website hosting via NGINX

• Free TLS(SSL) certificates from Let’s Encrypt

• Web administration

• Spam filtering, greylisting

• Host email for multiple users and multiple domain names

Mail-in-a-Box system requirements: Ubuntu 18.04 64-bit, 512MB RAM (recommend 1GB RAM)

Mail-in-a-Box

4. iRedMail

iRedMail is an open source mail server since 2007. It works on most Linux/BSD distributions. It offer paid version ($499/year) with professional support.

iRedMail features:

• Web admin panel (paid professional version available)

• Support different backend storages: OpenLDAP, MySQL, MariaDB, PostgreSQL

• Works on main stream Linux/BSD: Red Hat, CentOS, Debian, Ubuntu, FreeBSD, OpenBSD.

• SpamAssassin, ClamAV, SPF, DKIM, greylisting, whitelisting, blacklisting

• Roundcube webmail or SOGo groupware

• CalDAV, CardDAV and ActieSync

• Unlimited mail accounts, domains, users, mailing lists, admins

• Paid professional support available

iRedMail system requirements: Fresh Linux/BSD server, 2GB RAM

iRedMail

5. Modoboa

Modoboa is a free and open source email hosting and management platform that support SMTP, IMAP/POP. It is written in Python and released under ISC license.

Modoboa features:

• Web admin panel to manage domains, mailboxes, aliases and more

• Support MySQL/MariaDB, PostgreSQL database

• Email blacklists monitoring and DMARC report generation

• Mail server monitoring

• Own web mail client

• Anti-spam and anti-virus via Amavis

• Calendar and address book

• Free SSL/TLS certificates by Let’s Encrypt

• Paid professional support available

SubAddressing (Release Note)

• SubAddressing uses a ‘+’ as part of the destination user

• a great way to filter emails out of your inbox without having to configure filters for each sender.

• For example, if I’m signing up for an account at a delivery service to send my mum a bouquet for Mother's Day, I can use the email address adam+flowerdelivery@domain.tld to filter future “offer” emails into a folder named ‘flowerdelivery’ at my email account adam@domain.tld. This has the additional feature of allowing you to track who is sharing your email address with other companies as well, since each address acts as a unique address.

IMAP Full-Text Search Indexing

• (powered by Solr) provides incredibly fast searching for all of your email hosted on a cPanel & WHM server over an IMAP connection.

• As an email user you will immediately notice that searching your email is blazing fast, even if your email is hosted on the server.

• It’s also true for any iOS device, Microsoft Outlook®, SquirrelMail, Horde, Roundcube, and Mozilla Thunderbird.

• enable it via the WHM’s Manage Plugins interface (Home >> cPanel >> Manage Plugins), or by running the install_dovecot_fts (full text search) script.