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Slow Mail vs K-9 Mail: catalog facts
Slow Mail	K-9 Mail
Free Free and open source under the MIT licence.	Free Free and open source.
Android	Android
No emails or message lists stored on the device Works with any IMAP and SMTP provider	Open source with a long track record on Android Now the foundation for Thunderbird's official mobile app
Needs an active internet connection to read mail Slower than clients with a local cache	Android only, no iOS version Interface is more utilitarian than modern polished mail apps
Downloadable app	Downloadable app
Open source	Open source
License: MIT	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.