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BlueMail vs K-9 Mail: catalog facts
BlueMail	K-9 Mail
Freemium The client is free to download. Some features are reserved for paid plans.	Free Free and open source.
Windows, macOS, Linux, iOS	Android
One inbox covers many accounts across Windows, macOS, Linux, Android and iOS with a consistent interface and shared…	Open source with a long track record on Android Now the foundation for Thunderbird's official mobile app
It is closed source, some features need a paid plan, and its handling of account credentials has drawn…	Android only, no iOS version Interface is more utilitarian than modern polished mail apps
Downloadable app	Downloadable app
Closed source	Open source
License not stated	License: Apache-2.0
Not stated if an account is needed	Not stated if an account is needed
Not stated if it works offline	Not stated if it works offline
Official website Full listing and sources Checked September 22, 2026	Official website Full listing and sources Checked September 22, 2026

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