Software

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

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))

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://github.com/OpenSMTPD/OpenSMTPD/))

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 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/))