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K-9 Mail vs Aqua Mail: catalog facts
K-9 Mail	Aqua Mail
Free Free and open source.	Freemium Free to try, with a paid purchase that removes ads and unlocks more features.
Android	Android
Open source with a long track record on Android Now the foundation for Thunderbird's official mobile app	Works with any IMAP or POP3 account alongside the major providers Does not route mail or passwords through its own cloud
Android only, no iOS version Interface is more utilitarian than modern polished mail apps	Free version shows ads Android only
Downloadable app	Downloadable app
Open source	Closed source
License: Apache-2.0	License not stated
Not stated if an account is needed	No account 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 23, 2026

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