Compare software

SmarterMailCitadel
Freemium

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

 Free

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

Windows, Linux, Web, Self-hosted Web, Self-hosted
  • Native MAPI support for Outlook without plug-ins
  • Calendars, contacts, tasks, chat and meetings included
  • Mail, calendar, contacts, forums, wiki and chat in one server
  • Consistent rooms-based structure across features
  • Proprietary, closed-source software
  • Running a mail server requires ongoing administration
  • The rooms metaphor differs from conventional mail servers
  • Requires running and maintaining your own server
Downloadable app, Self-hosted Self-hosted
Closed source Open source
License not stated License: GPL
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 1, 2026

Checked October 2, 2026

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