Compare software

CitadelSmarterMail
Free

Free and open source under the GNU GPL, with no paid edition.

 Freemium

Can be downloaded for free, with paid licences available to buy.

Web, Self-hosted Windows, Linux, Web, Self-hosted
  • Mail, calendar, contacts, forums, wiki and chat in one server
  • Consistent rooms-based structure across features
  • Native MAPI support for Outlook without plug-ins
  • Calendars, contacts, tasks, chat and meetings included
  • The rooms metaphor differs from conventional mail servers
  • Requires running and maintaining your own server
  • Proprietary, closed-source software
  • Running a mail server requires ongoing administration
Self-hosted Downloadable app, Self-hosted
Open source Closed source
License: GPL License not stated
Not stated if an account is needed Not stated if an account is needed
Not stated if it works offline Not stated if it works offline

Checked October 2, 2026

Checked October 1, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.