Open-source Fastmail 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.

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.

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.

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.

Forward Email is an open-source email service focused on privacy. It handles custom-domain email forwarding and also provides mailboxes accessible over IMAP, POP and SMTP, with encryption using algorithms such as AES-256 and ChaCha20, and it positions itself as an all-in-one alternative to Gmail, Mailchimp and Sendgrid.

Its topics and documentation point to features such as sending mail, newsletters, SQLite-based storage, push notifications, and calendar and contact support through CalDAV and CardDAV, plus autodiscovery records and Domain Connect integration for setting up DNS. The README includes a local development guide and detailed notes on server infrastructure, load balancing, provisioning and deployment, including automated setup with Ansible.

The code is JavaScript and the project says it is fully open source, so the service can be inspected and, with the published infrastructure guidance, run on your own servers. Most consumers simply use the hosted service at forwardemail.net. It suits individuals and small organizations that want private email on their own domain and developers interested in how such a stack is built.