Instead of Microsoft Outlook
Mail, calendar and contacts for Microsoft accounts.
Mail and calendar move together, which makes this simpler than it looks. Exchange's shared-mailbox behaviour is the piece most alternatives do badly.
You lose: Shared calendars and mailboxes that just work, and the Outlook mobile app.
Start here
Mailcow
Includes SOGo for calendar and contacts. Interface is functional, not pretty.
github.com/mailcow/mailcow-dockerizedmailcow.email
A database, object storage or mail config, plus backups.
Also worth a look
- Stalwart
Mail, calendar and contacts in one service. Shared mailboxes are newer than Exchange's.
- Mailu
Lean. You add a groupware suite separately.
What the desk has written
Facts checked 8 November 2026. Licences, activity and archive status come from each project's own repository; the verdict and the cost lines are the desk's.