Open-source Gmail alternatives

Docker Mailserver runs a complete mail server inside a container. It bundles SMTP and IMAP services (Postfix and Dovecot, according to the project topics), optional LDAP authentication, and anti-spam and anti-virus tooling, so a self-hoster does not have to assemble each piece separately.

The design is deliberately simple: it uses configuration files only, with no SQL database, which keeps setups easy to version, deploy and upgrade. Related topics include fail2ban and Rspamd. The documentation covers initial setup, environment variables, updating and an FAQ, and the project asks users to match the documentation version to the image version they run.

Docker Mailserver is released under the MIT license and has been maintained by volunteers since January 2021. It is a self-hosting project with no hosted offering, suited to administrators who want to run their own mail on a server they control.

Mail-in-a-Box helps individuals take back control of their email by providing a one-click, easy-to-deploy mail server in a box. It turns a fresh Ubuntu 22.04 LTS 64-bit machine into a working mail server by installing and configuring the required components. There are no user-configurable setup options, so it is designed to just work.

The installed components include Postfix for SMTP, Dovecot for IMAP, Nextcloud for CardDAV and CalDAV, z-push for Exchange ActiveSync, and Roundcube webmail. It adds spam filtering with SpamAssassin and greylisting with Postgrey, DNS with SPF, DKIM, DMARC, DNSSEC, DANE TLSA, MTA-STS and SSHFP records set automatically, and TLS certificates from Let's Encrypt. Backups use duplicity, with ufw, fail2ban and munin for protection and monitoring.

Project goals include making a good mail server easy to deploy, promoting decentralization and privacy, and keeping configuration automated, auditable and idempotent. It deliberately does not aim to be customizable by power users. Mail-in-a-Box is written in Python, released into the public domain under CC0-1.0, and has a Code of Conduct for contributors.

Stalwart is an open-source mail and collaboration server written in Rust and designed to be secure, fast, robust and scalable. It supports JMAP, IMAP4, POP3, SMTP, CalDAV, CardDAV and WebDAV, so a single server can handle email, calendars, contacts and file storage.

On the email side it offers JMAP for Mail and Sieve, IMAP4rev2 and IMAP4rev1 with ManageSieve, and POP3. The SMTP server includes DMARC, DKIM, SPF and ARC for message authentication, transport security through DANE, MTA-STS and TLS reporting, automated DKIM key rotation, throttling and filtering rules, sieve scripting and milter integration, and distributed virtual queues.

The collaboration features cover CalDAV and JMAP for Calendars, CardDAV and JMAP for Contacts, and WebDAV and JMAP for File Storage, with fine-grained sharing through WebDAV ACL and JMAP Sharing. A built-in spam and phishing filter includes a rule set and LLM-driven message analysis. It is self-hosted software that administrators run on their own servers.

Thunderbird for Android is an open-source email app for Android that manages multiple email accounts from one place, with an optional Unified Inbox. It is the Android edition of Thunderbird, developed by a team of developers with help from a community of volunteers, and it is based on K-9 Mail, formerly the project's name. It is written in Kotlin.

The project states that Thunderbird never treats private data as a product. The app can be installed from Google Play or F-Droid, in stable or beta versions, from GitHub releases, through FFUpdater, or with Obtainium. The beta channel gives early access to features still under development, and signing certificate fingerprints are published in the security document.

Help comes from a knowledge base, a support forum and a GitHub issue tracker, and feature ideas are discussed on connect.mozilla.org. Release notes describe what changed in each version. The app is released under the Apache 2.0 license and runs on the phone itself, connecting to the email providers you configure.

mailcow: dockerized is an open-source mail server package that runs as a set of Docker containers managed with Docker Compose. It bundles the pieces needed to run your own email, so administrators do not have to assemble and configure each component separately.

The stack is built around established open-source software: Postfix for SMTP, Dovecot for IMAP, Rspamd for spam filtering, ClamAV for antivirus scanning, SOGo for groupware and webmail, and ACME support for certificates. A web administration interface sits on top. Topics in the repository also mention the Olefy component for document scanning.

mailcow is released under the GNU General Public License v3 and installed on your own server following the official documentation. It is managed and maintained by The Infrastructure Company GmbH, and the project offers support contracts through Servercow as well as a one-time support payment option. The community gathers on Telegram, Mastodon and GitHub Sponsors.

Tuta, formerly known as Tutanota, is an email service built around security and privacy. It uses built-in end-to-end encryption to protect emails, contacts and calendar entries across devices, and it lets users communicate securely with other people regardless of what provider they use.

The open-source repository contains the client applications, which include a web client, an iOS app and a desktop client, along with separate calendar releases for mobile platforms. The code is written in TypeScript and JavaScript on top of the Mithril framework and is licensed under GPL-3.0. Build, translation and development instructions are provided in dedicated files, and the roadmap and feature requests are handled through Reddit and the vendor website.

Tuta is a hosted service operated by the vendor rather than a product you install on your own server. The repository states that it does not accept contributions or bug reports produced with the help of large language models, and maintainers close such submissions without explanation.

Mailu is a full-featured mail server delivered as a set of Docker images. The project aims to give people an easily set up and maintained mail server made entirely of free software, without proprietary components or unrelated groupware features and without trackers.

It covers the standard email server functions, IMAP and SMTP with client auto-configuration profiles, along with aliases, domain aliases, custom routing and full-text search of attachments. Users get webmail, auto-reply, auto-forward and managesieve, while admins get global admin roles, per-domain delegation, announcements and quotas. Security features include enforced TLS, DANE, MTA-STS, Let's Encrypt certificates, outgoing DKIM and an antivirus scanner, and antispam features include greylisting, auto-learning, DMARC, SPF and anti-spoofing checks.

Mailu is written in Python and deployed with Docker or Docker Compose. The project's own configuration files, Dockerfiles and code are MIT-licensed, and all bundled components are free software compatible with it. A demo server and website documentation are provided.

Roundcube Webmail is a multilingual IMAP client that runs in the browser and behaves like a desktop application. It offers the functions people expect from an email client, such as MIME support, an address book, folder management, message search and spell checking, without installing anything on their own computers.

It is written in PHP and JavaScript and requires MariaDB, MySQL, PostgreSQL or SQLite as its database. A plugin API makes it extensible, and the user interface can be customized with skins. The client uses jQuery 3.x and inherits its browser support, covering current versions of Chrome, Edge, Firefox and Safari. Releases follow semantic versioning, and the README ships separate install and upgrade guides.

Roundcube is licensed under GPL-3.0 and is installed on a web server that connects to an existing IMAP mail server. Note that the repository README warns that the Git snapshot is not a stable version and should not replace a production installation.

Maddy Mail Server is a composable all-in-one mail server written in Go. It implements the functions needed to run an email server: it sends messages over SMTP as an MTA, accepts messages over SMTP as an MX and stores messages while providing access to them over IMAP.

It also implements the auxiliary protocols needed to keep email reasonably secure, including DKIM, SPF, DMARC, DANE and MTA-STS. The project positions itself as a replacement for a stack made of Postfix, Dovecot, OpenDKIM, OpenSPF, OpenDMARC and similar tools, using one daemon with a uniform configuration and low maintenance cost.

The README is candid that IMAP storage is still in beta. For a stable and feature-rich implementation of that part, the maintainers suggest using Dovecot instead, and Maddy can still handle message delivery. Maddy is licensed under GPL-3.0, and a setup tutorial, documentation, an IRC channel and a mailing list are available.

Mox is a mail server for people who want to run email for their own domains with little ongoing effort. It aims to be quick to start and to maintain, and it bundles the pieces of an email stack in one program.

Features include SMTP for receiving, submitting and delivering mail, IMAP4 for client access, and webmail in the browser. Authentication covers SPF, DKIM and DMARC, including DMARC aggregate reports. Spam handling is based on per-user reputation tracking and Bayesian filtering, and senders with low reputation can be slowed down, similar to greylisting. It supports internationalized email, automatic TLS via ACME for Let's Encrypt, DANE and MTA-STS with TLSRPT reporting, and account autodiscovery. A web admin interface helps set up domains, accounts and aliases and shows the DNS records to create.

Mox is written in Go and licensed under MIT. It is self-hosted software, and the project website provides details and a quickstart.