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Aqua Mail vs K-9 Mail: catalog facts
Aqua Mail	K-9 Mail
Freemium Free to try, with a paid purchase that removes ads and unlocks more features.	Free Free and open source.
Android	Android
Works with any IMAP or POP3 account alongside the major providers Does not route mail or passwords through its own cloud	Open source with a long track record on Android Now the foundation for Thunderbird's official mobile app
Free version shows ads Android only	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
No account 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 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.