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Thunderbird vs Mailbird: catalog facts
Thunderbird	Mailbird
Free Free forever, funded by donations.	Paid Paid desktop app, sold as a one-time or subscription license.
Windows, macOS, Linux, Android	Windows, macOS
Unified inbox across every account, or each account kept separate, your choice Mail, calendar, contacts and tasks in one application rather than four	Unifies multiple email accounts and providers into one inbox App integrations reduce the need to switch to separate tools
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	Windows and macOS only Full feature set requires a paid license
Downloadable app	Downloadable app
Open source	Closed source
License: MPL-2.0	License not stated
No account needed	Not stated if an account is needed
Works offline	Not stated if it works offline
Official website Full listing and sources Checked September 20, 2026	Official website Full listing and sources Checked September 22, 2026

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