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Nine vs K-9 Mail: catalog facts
Nine	K-9 Mail
Paid Pricing is not listed on the homepage; check the store listing for current terms.	Free Free and open source.
Android, iOS	Android
Direct Push sync with Exchange ActiveSync servers Mail, calendar, contacts, tasks and notes in one app	Open source with a long track record on Android Now the foundation for Thunderbird's official mobile app
IMAP accounts sync email only Pricing not stated on the homepage	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 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.