Software

Zulip is a powerful, open source group chat application. ([Source Code](https://github.com/zulip/zulip))

Email forwarding service for creating aliases. ([Source Code](https://github.com/anonaddy/anonaddy))

Complete email solution that runs on any webspace with PHP and MariaDB. It supports POP3 catchall mailboxes and can also integrate with Postfix or b1gMailServer if you're running your own server. ([Source Code](https://codeberg.org/b1gMail/b1gMail), [Clients](https://www.b1gmail.eu/en/start/addon-b1gmailserver/))

Your Debian-based data center in a box. A set of general-purpose Ansible roles that can be used to manage Debian or Ubuntu hosts. ([Source Code](https://github.com/debops/debops))

Production-ready fullstack but simple mail server (SMTP, IMAP, LDAP, Antispam, Antivirus, etc.) running inside a container. Only configuration files, no SQL database. ([Source Code](https://github.com/docker-mailserver/docker-mailserver))

SMTP server that sends and receives emails according to a simple configuration file, with an optional web interface that you can use to browse your emails. ([Source Code](https://dovel.email/server/tree.html))

Luke Smith's bash script to completely automate the setup of a Postfix/Dovecot/SpamAssassin/OpenDKIM server on debian

Lets you have an infinite number of unique inboxes. ([Source Code](https://codeberg.org/Inboxen/Inboxen))

Full-featured mail server solution based on Postfix and Dovecot. ([Source Code](https://github.com/iredmail/iRedMail))

All-in-one mail server that implements SMTP (both MTA and MX) and IMAP. Replaces Postfix, Dovecot, OpenDKIM, OpenSPF, OpenDMARC with single daemon. ([Source Code](https://github.com/foxcpp/maddy))

Turns any Ubuntu server into a fully functional mail server with one command. ([Source Code](https://github.com/mail-in-a-box/mailinabox))

Mail server suite based on Dovecot, Postfix and other open source software, that provides a modern Web UI for administration. ([Source Code](https://github.com/mailcow/mailcow-dockerized))

Simple yet full-featured mail server as a set of Docker images. ([Source Code](https://github.com/Mailu/Mailu))

Mail hosting and management platform including a modern and simplified web user interface. ([Source Code](https://github.com/modoboa/modoboa))

Complete e-mail solution with IMAP4, SMTP, SPF, DKIM, DMARC, MTA-STS, DANE and DNSSEC, reputation-based and content-based junk filtering, Internationalization (IDNA), automatic TLS with ACME and Let's Encrypt, account autoconfiguration, and webmail. ([Source Code](https://github.com/mjl-/mox))

Complete and fully featured mail server for use by websites & web servers. ([Source Code](https://github.com/postalserver/postal))

Complete mailserver solution leveraging the Nix Ecosystem

Open source email alias solution to protect your email address. Comes with browser extensions and mobile apps. ([Source Code](https://github.com/simple-login/app))

All-in-one mail server with JMAP, IMAP4, and SMTP support and a wide range of modern features. ([Source Code](https://github.com/stalwartlabs/stalwart))

Scalable no-SPOF IMAP/POP3 mail server. ([Source Code](https://github.com/zone-eu/wildduck))

Email (IMAP/POP3), contacts and calendar server. ([Source Code](https://github.com/cyrusimap/cyrus-imapd))

IMAP and POP3 server written primarily with security in mind. ([Source Code](https://github.com/dovecot/core))

SMTP (email) server with a focus on simplicity, security, and ease of operation. ([Source Code](https://blitiri.com.ar/git/r/chasquid/))

Fast, scalable, enterprise mail/groupware server providing ESMTP, IMAP, POP3, webmail, mailing list, basic web-based calendaring and scheduling services. ([Source Code](https://www.courier-mta.org/repo.html))