Software

A small MTA for home and office use. Works on Linux and FreeBSD

A small and easy to configure SMTP and POP3 server for Windows and Linux. ([Source Code](https://sourceforge.net/p/emailrelay/code/HEAD/tree/))

Message transfer agent (MTA) developed at the University of Cambridge. ([Source Code](https://git.exim.org/exim.git))

Fast, highly extensible, and event driven SMTP server. ([Source Code](https://github.com/haraka/Haraka))

Secure SMTP server implementation from the OpenBSD project. ([Source Code](https://cvsweb.openbsd.org/cgi-bin/cvsweb/src/usr.sbin/smtpd/))

Complete trashmail solution that exposes an SMTP server and has a web interface to manage received emails. Works with multiple and wildcard domains and is fully file based (no database needed). Includes RSS feeds and JSON API

Fast, easy to administer, and secure Sendmail replacement

Message transfer agent (MTA)

Access GNU Mailman v3 archives. ([Demo](https://lists.mailman3.org/), [Source Code](https://gitlab.com/mailman/hyperkitty))

Reliable and easy-to-use newsletter tool (alternative to Mailchimp and Sendinblue). ([Demo](https://app.keila.io), [Source Code](https://github.com/pentacent/keila))

High performance, self-hosted newsletter and mailing list manager with a modern dashboard. ([Demo](https://demo.listmonk.app/), [Source Code](https://github.com/knadh/listmonk))

Manage electronic mail discussion and e-newsletter lists. ([Source Code](https://gitlab.com/mailman/))

Marketing automation software (email, social and more). ([Source Code](https://github.com/mautic/mautic))

Newsletter and email marketing with advanced management of subscribers, bounces, and plugins. ([Source Code](https://github.com/phpList/phplist3))

Web user interface to access GNU Mailman. ([Source Code](https://gitlab.com/mailman/postorius/))

GPG-enabled mailing list manager with resending-capabilities. ([Source Code](https://0xacab.org/schleuder/schleuder/tree/master))

Mailing list manager. ([Source Code](https://github.com/sympa-community/sympa))

Feed reader for your email accounts. ([Source Code](https://github.com/cypht-org/cypht))

Browser-based IMAP client with an application-like user interface. ([Source Code](https://github.com/roundcube/roundcubemail))

Simple, modern, lightweight & fast web-based email client (fork of RainLoop). ([Demo](https://snappymail.eu/demo/), [Source Code](https://github.com/the-djmaze/snappymail), [Clients](https://snappymail.eu/repository/v2/plugins/))

Another browser-based IMAP client. ([Source Code](https://sourceforge.net/p/squirrelmail/code/HEAD/tree/))

Modern IRCv3 server written in Go, combining the features of an ircd, a services framework, and a bouncer. ([Source Code](https://github.com/ergochat/ergo))

A web frontend for WeeChat. ([Demo](https://www.glowing-bear.org))

Modular IRC server written in C++ for Linux, BSD, Windows, and macOS. ([Source Code](https://github.com/inspircd/inspircd))