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KMail vs Betterbird: catalog facts
KMail	Betterbird
Free Free and open source under the GPL.	Free Free and open source, funded by donations.
Linux	Windows, macOS, Linux
OpenPGP and S/MIME encryption integrated rather than bolted on Shares contacts and calendar with the rest of the Kontact suite	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
Depends on the Akonadi storage service, which is a common source of problems Linux only in practice	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
Downloadable app	Downloadable app
Open source	Open source
License: GPL-2.0	License: MPL-2.0
Not stated if an account is needed	No account needed
Not stated if it works offline	Works offline
Official website Full listing and sources Checked September 22, 2026	Official website Full listing and sources Checked September 20, 2026

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