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Claws MailThunderbird
Free

Free and open source under the GPL 3.0 or later.

 Free

Free forever, funded by donations.

Windows, macOS, Linux Windows, macOS, Linux, Android
  • Opens and searches enormous mail folders without stalling
  • Plugins for PGP, spam filtering, RSS and calendars ship with it
  • Unified inbox across every account, or each account kept separate, your choice
  • Mail, calendar, contacts and tasks in one application rather than four
  • Composes plain text by default; HTML mail sending is deliberately limited
  • The interface is functional and looks like it was designed in 2004
  • The interface carries a lot of history and can feel dense next to a webmail tab
  • Major ESR releases have historically been disruptive for add-ons and settings
Downloadable app Downloadable app
Open source Open source
License: GPL-3.0-or-later License: MPL-2.0
No account needed No account needed
Works offline Works offline

Checked September 21, 2026

Checked September 20, 2026

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