K-9 Mail suits people who want one email app for several accounts and who care about what an app does with their data. It is free, carries no ads and is released under the Apache-2.0 licence. Version 24.0 needs Android 6.0 or newer and takes up 10.4 MB.
Who K-9 Mail fits, and who it does not
The app is aimed at users who run more than one mailbox, for example a personal and a work address, and want them in one place. Because it is described as working with basically every email provider, it is not tied to a single service. People who prefer an open codebase will also find the source on GitHub under the Thunderbird Android project.
It is a plain email client. If you are looking for chat or social features, the catalog lists other apps for that, and K-9 Mail does not try to cover them.
Unified Inbox, sync and search in daily use
Multiple accounts are supported, and the Unified Inbox combines them into a single list so you do not have to switch between mailboxes. Mail arrives through automatic background synchronization or push notifications, depending on what you set up.
Search works in two ways: locally on the device and on the server. That matters when an older message is no longer stored on the phone but still sits with your provider.
The app was first released on September 12, 2013, and the latest update in our records is from October 18, 2026.
OpenPGP encryption needs a second app
K-9 Mail supports OpenPGP email encryption using PGP/MIME. The store description points to OpenKeychain: Easy PGP as the app to install for encrypting and decrypting messages, so the feature is not self-contained.
The app is described as privacy-friendly, with no tracking and connections only to your email provider. Support runs through a community forum, and the project invites developers, designers, translators and bug triagers to contribute.
Costs and size
K-9 Mail costs nothing and shows no ads. At 10.4 MB it is a light download for an email client.
The project keeps a website at k9mail.app.
K-9 Mail pros and cons
Pros
- Free, with no ads and an Apache-2.0 licence
- Unified Inbox across multiple accounts
- Local and server-side search
- OpenPGP (PGP/MIME) encryption support
- Small 10.4 MB download
Cons
- PGP encryption relies on the separate OpenKeychain app
- Developer name is not shown on the listing
- Requires Android 6.0 or newer
- No Google Play rating or install count to go by
Is K-9 Mail safe?
This is the unmodified APK of K-9 Mail (package com.fsck.k9). To verify the download, compare its SHA-256 checksum with 0f9dd57fbd06dddfd8bcf7de6106d27fa0f0297793193828c4eac904518b1e05. The source code is public on GitHub under the Apache-2.0 license, and the app describes itself as connecting only to your email provider, with no tracking. No developer name is listed, so the checksum is the most reliable way to confirm the file.
How to install K-9 Mail
- Download the APK with the button on this page and wait for it to finish.
- Compare the file with the SHA-256 checksum shown here if you want to confirm it arrived intact.
- Open the file on your phone and allow installs from this source when Android asks.
- Finish the install, then open K-9 Mail from your app drawer.
