K-9 Mail is an open source email client focused on making it easy to chew through large volumes of email. Designed for both novice and power users and offers lots of features for everyone.
Android - K-9 Mail
Official website k9mail.app
Our take
If you have a pile of accounts and you live in your inbox on Android, K-9 Mail handles high volume better than the polished consumer clients, and it is open source with a long track record. It is not itself a private email provider, it is a client, so your privacy still comes from the server you connect it to. The interface looks its age and there is a learning curve; people who want something that just looks nice should consider its successor, Thunderbird for Android.
GitHub at a glance
thunderbird/thunderbird-android
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13,626
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Last commit
1d ago
healthy
License
Apache-2.0
Latest release
THUNDERBIRD_19_2
15d ago
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Android - K-9 Mail license, in plain English
Apache-2.0 Permissive
Permissive like MIT, with an explicit patent grant and a requirement to flag any changes you make.
Permits
- Commercial use
- Modification
- Distribution
- Patent use
- Private use
Requires
- License and copyright notice
- State changes
Does not provide
- Trademark use
- Liability cover
- Warranty
Why it matters: Permissive licensing lets anyone reuse this, including inside closed products. That is freedom to build on, but no guarantee that downstream copies stay open.
Plain-language summary of the project's license, not legal advice. Read the full text for the exact terms.