Production-ready mail server stack in a Docker container with SMTP, IMAP/POP3, LDAP auth, anti-spam/AV, DKIM/DMARC, and optional OAuth2 support.
18.8k stars2k forksMITlast commit Actively maintained
20 self-hosted Zimbra Collaboration alternatives
Cloud-hosted email and collaboration platform providing IMAP/SMTP mail, webmail, calendaring, contacts, tasks and file sharing, with groupware features and admin tools for secure organizational messaging and collaboration.
Alternatives to Zimbra Collaboration
Mail-in-a-Box is a one-click mail server appliance for Ubuntu, bundling SMTP/IMAP, webmail, DNS, TLS automation, backups, and an admin control panel.
15.4k stars1.5k forksCC0-1.0last commit Actively maintained
All-in-one open-source mail and collaboration server with SMTP, IMAP, JMAP, CalDAV, CardDAV, and WebDAV, plus integrated anti-spam and phishing protection.
14.4k stars909 forkslast commit Actively maintained
Mailcow is a dockerized mail server suite providing SMTP/IMAP, webmail, anti-spam/anti-virus, and domain/mailbox administration via a unified web UI.
13.3k stars1.8k forksGPL-3.0last commit Actively maintained
#5
Mailu is a full-featured mail server distributed as Docker images, providing SMTP/IMAP/POP3, webmail, administration UI, and built-in security and anti-spam features.
7.5k stars997 forkslast commit Actively maintained
Open source webmail client for IMAP with address book, search, folders, and a customizable UI via plugins and skins.
7.1k stars1.8k forksGPL-3.0last commit Actively maintained
#7
All-in-one secure mail server with SMTP, IMAP, webmail, automatic TLS (ACME), and built-in SPF/DKIM/DMARC plus junk filtering for low-maintenance domains.
5.8k stars218 forksMITlast commit Actively maintained
#8
Lightweight CalDAV/CardDAV server for syncing calendars, to-dos, and contacts with many clients, storing data on the filesystem and supporting auth and TLS.
4.9k stars521 forksGPL-3.0last commit Actively maintained
#9
Modoboa is an open source mail server management platform with a modern web UI, integrating Postfix and Dovecot with admin tools, webmail, calendar, and address book.
3.5k stars481 forksISClast commit Actively maintained
#10
Open source groupware suite providing webmail, calendaring, address books, and shared resources via open standards like IMAP, CalDAV, and CardDAV.
2.2k stars320 forksGPL-2.0last commit Actively maintained
#11
Automated open-source mail server installer bundling Postfix, Dovecot, webmail, anti-spam/antivirus and LDAP/SQL backends for mainstream Linux/BSD.
1.8k stars260 forksGPL-3.0last commit Actively maintained
#12
EteSync (Etebase Server) provides a self-hostable, zero-knowledge, end-to-end encrypted sync backend for calendars, contacts, tasks and notes across devices.
1.8k stars102 forksAGPL-3.0last commit Likely dormant
#13
sabre/dav is a PHP framework for building WebDAV file servers and CalDAV/CardDAV calendar and contacts services.
1.7k stars369 forksBSD-3-Clauselast commit Actively maintained
#14
High-performance, standards-compliant IMAP/POP3/LMTP server with flexible authentication, extensible plugin system (Lua, Sieve) and OpenSSL TLS support.
1.2k stars347 forkslast commit Actively maintained
Nextcloud Mail is a webmail app that connects to IMAP/SMTP accounts, offering a unified inbox and deep integration with other Nextcloud apps like Contacts and Calendar.
1k stars340 forksAGPL-3.0last commit Actively maintained
#16
Davis is a sabre/dav-based CalDAV/CardDAV/WebDAV server with a modern Symfony 7 admin dashboard for managing users, calendars, sharing, and address books.
743 stars46 forksMITlast commit Actively maintained
#17
Cyrus IMAP is a secure, scalable mail server providing IMAP/JMAP email plus CalDAV/CardDAV contacts and calendars, with ACLs, quotas, search, and replication.
643 stars175 forkslast commit Actively maintained
#18
Open-source, browser-based groupware providing calendar, email, file manager, CRM, projects, Collabora Online integration and SSO support.
295 stars113 forkslast commit Actively maintained
#19
Open-source PHP groupware providing CalDAV/CardDAV, ActiveSync, email client, CRM, tasks, file manager and Docker images for on-premise collaboration.
21 stars4 forksAGPL-3.0last commit Actively maintained
#20
Citadel is an open source groupware and messaging server providing email, calendars, contacts, and a web interface with room-based collaboration.
Activity unknown
What replacing Zimbra Collaboration actually involves
Every option on this page is open source and free to run on your own hardware, so you own the data and there is no subscription to cancel. 18 of 20 shipped a commit in the last six months. Licences in this list: MIT, CC0-1.0, GPL-3.0, ISC, GPL-2.0. In exchange you take on hosting, backups and updates yourself.
Browse everything in Email Servers (SMTP/IMAP).
