K-9 Mail
What K-9 Mail is
K-9 Mail is a free, open-source email client for Android, intended for novice and power users handling substantial mail volumes. It supports multiple accounts and works with basically every email provider. A unified inbox combines messages, while notifications can remain specific to each account. Synchronization can happen automatically in the background or through push notifications, and searches can run locally or on the server. OpenPGP email encryption uses PGP/MIME; OpenKeychain must be installed to encrypt or decrypt messages. The app also offers white and dark themes, signatures, message flagging, multiple identities, keyboard shortcuts, attachment saving, and offline access. It has no calendar tools and does not support scheduled sending. Downloads are offered through Google Play, F-Droid, and direct GitHub APKs. K-9 Mail is licensed under Apache License 2.0, with source code on GitHub. Its manual is abandoned, although a historic version remains available.
Who it suits
K-9 Mail suits Android users managing several accounts or large volumes of email, including both beginners and power users. It is also suited to people seeking local processing and OpenPGP support.
What it does well
- Free Android email client
- Unified inbox for multiple accounts
- Local and server-side search
- Offline access available
- OpenPGP support with OpenKeychain
What to know first
- Android-only platform
- No calendar tools
- No scheduled sending
- Current user manual abandoned
Plans
| Plan | Billed and limits | Price |
|---|---|---|
| K-9 Mail | Android email client · open source | Free |
As k9mail.app lists them, read 12 Oct 2026. The maker's own page has the final word.
Verdict
K-9 Mail provides a broad Android email feature set without a charge, including unified account handling, offline access, and encrypted-mail support. Its Android-only scope, absent calendar and scheduling tools, and outdated manual are important limitations.
Facts from K-9 Mail's own pages
- Accounts
- The app supports multiple accounts and works with basically every email provider. · play.google.com, 12 Oct 2026
- App coverage
- mobile · k9mail.app, 24 Sept 2026
- Audience
- The maker says K-9 Mail is designed for novice and power users. · k9mail.app, 12 Oct 2026
- Calendar tools
- No · k9mail.app, 24 Sept 2026
- Documentation
- The user manual page says the manual has been abandoned because the team lacks resources to keep it up to date; a historic version remains available. · docs.k9mail.app, 12 Oct 2026
- Downloads
- The maker lists Google Play, F-Droid and direct APK downloads from GitHub as download channels. · k9mail.app, 12 Oct 2026
- Encryption
- K-9 Mail supports OpenPGP email encryption using PGP/MIME, and the listing says to install OpenKeychain to encrypt or decrypt email. · play.google.com, 12 Oct 2026
- Free plan
- Yes · k9mail.app, 24 Sept 2026
- Inbox
- Features include a unified inbox and per-account notifications. · k9mail.app, 12 Oct 2026
- License
- K-9 Mail is licensed under Apache License, Version 2.0, and its source code is available on GitHub. · k9mail.app, 12 Oct 2026
- Local data
- The privacy notice says names, email messages and address books are stored and processed locally on the device and never sent to Mozilla. · k9mail.app, 12 Oct 2026
- OAuth
- The privacy notice says OAuth authentication and synchronization happen directly between the app and the provider over an encrypted connection, without Mozilla-operated services. · k9mail.app, 12 Oct 2026
- Other features
- The maker lists white and dark themes, signatures, message flagging, multiple identities, keyboard shortcuts and attachment saving. · k9mail.app, 12 Oct 2026
- Privacy
- The Google Play listing says the app shares no data with third parties and collects no data; it also says data is encrypted in transit. · play.google.com, 12 Oct 2026
- Purpose
- K-9 Mail is an open source email client for Android with advanced features, designed to help users manage large volumes of email. · k9mail.app, 12 Oct 2026
- Search
- The app supports local and server-side email search. · play.google.com, 12 Oct 2026
- Support
- The maker directs users with questions to its support forum and also lists Matrix and GitHub issue tracking for community interaction. · k9mail.app, 12 Oct 2026
- Synchronization
- The app supports automatic background synchronization or push notifications. · play.google.com, 12 Oct 2026
- Unified inbox
- Yes · k9mail.app, 24 Sept 2026
Where K-9 Mail stands on Freedom251
- Email clients#76 of 142