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K-9 Mail vs Nine: catalog facts
K-9 Mail	Nine
Free Free and open source.	Paid Pricing is not listed on the homepage; check the store listing for current terms.
Android	Android, iOS
Open source with a long track record on Android Now the foundation for Thunderbird's official mobile app	Direct Push sync with Exchange ActiveSync servers Mail, calendar, contacts, tasks and notes in one app
Android only, no iOS version Interface is more utilitarian than modern polished mail apps	IMAP accounts sync email only Pricing not stated on the homepage
Downloadable app	Downloadable app
Open source	Closed source
License: Apache-2.0	License not stated
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 23, 2026

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