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FairEmail vs K-9 Mail: catalog facts
FairEmail	K-9 Mail
Free Free to download from Google Play, F-Droid or GitHub releases.	Free Free and open source.
Android	Android
Works with nearly all IMAP providers and unlimited accounts OpenPGP and S/MIME encryption built in	Open source with a long track record on Android Now the foundation for Thunderbird's official mobile app
No Microsoft Exchange Web Services or ActiveSync support Android only	Android only, no iOS version Interface is more utilitarian than modern polished mail apps
Downloadable app	Downloadable app
Open source	Open source
License: GPL-3.0	License: Apache-2.0
Not stated if an account is needed	Not stated if an account is needed
Works offline	Not stated if it works offline
Official website Full listing and sources Checked September 23, 2026	Official website Full listing and sources Checked September 22, 2026

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