Open-source alternatives to Microsoft 365
2 open-source and self-hostable projects you can use instead of Microsoft 365, with license, free-edition limits and setup checked against official sources.
- Stalwart Mail ServerAlternative to Google Workspace, Microsoft 365
An all-in-one mail and collaboration server written in Rust, with JMAP, IMAP, POP3, SMTP, CalDAV, CardDAV and WebDAV, offered in a free Community edition and a paid Enterprise edition.
AGPL-3.0Self-hosted15kGitHub starsSome features paywalled - mailcowAlternative to Google Workspace, Microsoft 365
A Docker-based mail server suite that bundles Postfix, Dovecot, Rspamd, SOGo webmail and a web admin interface.
GPL-3.0Self-hostedCloud14kGitHub starsNot yet assessed
- Stalwart Mail Server — It can replace Exchange Online style email, calendar and contact hosting with a self-run server that clients reach over standard protocols.
- mailcow — It can replace Exchange Online style mailbox hosting for your own domains with a self-run mail server.