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AerionThunderbird
Free

Free and open source under the Apache 2.0 licence.

 Free

Free forever, funded by donations.

Windows, macOS, Linux Windows, macOS, Linux, Android
  • Built with Wails instead of Electron for lower resource use
  • Direct IMAP and SMTP connection with mail stored locally
  • Unified inbox across every account, or each account kept separate, your choice
  • Mail, calendar, contacts and tasks in one application rather than four
  • Young project with a smaller feature set than established clients
  • Tracking protection is described as basic
  • 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: Apache-2.0 License: MPL-2.0
No account needed No account needed
Not stated if it works offline Works offline

Checked October 1, 2026

Checked September 20, 2026

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