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Betterbird vs KMail: catalog facts
Betterbird	KMail
Free Free and open source, funded by donations.	Free Free and open source under the GPL.
Windows, macOS, Linux	Linux
Fixes and features Thunderbird has not shipped, listed openly in a comparison table Installs next to Thunderbird and runs on the same profile, so switching back is trivial	OpenPGP and S/MIME encryption integrated rather than bolted on Shares contacts and calendar with the rest of the Kontact suite
A small volunteer project riding on someone else’s release train The Mac build ships in English only and needs a language pack for anything else	Depends on the Akonadi storage service, which is a common source of problems Linux only in practice
Downloadable app	Downloadable app
Open source	Open source
License: MPL-2.0	License: GPL-2.0
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.