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Ltt.rs vs K-9 Mail: catalog facts
Ltt.rs	K-9 Mail
Free Free and open source under the Apache 2.0 licence.	Free Free and open source.
Android	Android
Native JMAP support Simple, focused interface	Open source with a long track record on Android Now the foundation for Thunderbird's official mobile app
Works only with JMAP servers, not IMAP Described as a proof of concept	Android only, no iOS version Interface is more utilitarian than modern polished mail apps
Downloadable app	Downloadable app
Open source	Open source
License: Apache-2.0	License: Apache-2.0
Not stated if an account is needed	Not stated if an account is needed
Needs internet	Not stated if it works offline
Official website Full listing and sources Checked October 2, 2026	Official website Full listing and sources Checked September 22, 2026

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