K-9 Mail
3.4star
99.8K reviews
Rated for 3+
info
5M+
Downloads
About this app
K-9 Mail is an open source email client that works with basically every email provider.
Features
* supports multiple accounts
* Unified Inbox
* privacy-friendly (no tracking whatsoever, only connects to your email provider)
* automatic background synchronization or push notifications
* local and server-side search
* OpenPGP email encryption (PGP/MIME)
Install the app "OpenKeychain: Easy PGP" to encrypt/decrypt your emails using OpenPGP.
Support
If you're having trouble with K-9 Mail, ask for help in our support forum at https://forum.k9mail.app
Want to help?
K-9 Mail is now part of the Thunderbird family and remains a community developed project. If you're interested in helping to improve the app, please join us! You can find our bug tracker, source code, and wiki at https://github.com/thunderbird/thunderbird-android
We're always happy to welcome new developers, designers, documenters, translators, bug triagers and friends.
Features
* supports multiple accounts
* Unified Inbox
* privacy-friendly (no tracking whatsoever, only connects to your email provider)
* automatic background synchronization or push notifications
* local and server-side search
* OpenPGP email encryption (PGP/MIME)
Install the app "OpenKeychain: Easy PGP" to encrypt/decrypt your emails using OpenPGP.
Support
If you're having trouble with K-9 Mail, ask for help in our support forum at https://forum.k9mail.app
Want to help?
K-9 Mail is now part of the Thunderbird family and remains a community developed project. If you're interested in helping to improve the app, please join us! You can find our bug tracker, source code, and wiki at https://github.com/thunderbird/thunderbird-android
We're always happy to welcome new developers, designers, documenters, translators, bug triagers and friends.
Updated on
Safety starts with understanding how developers collect and share your data. Data privacy and security practices may vary based on your use, region, and age. The developer provided this information and may update it over time.
No data shared with third parties
Learn more about how developers declare sharing
No data collected
Learn more about how developers declare collection
Data is encrypted in transit
Data can’t be deleted
Ratings and reviews
3.4
94.6K reviews
warcroft
- Flag inappropriate
June 3, 2026
I've been using K9 for quite a while now. But the last few months I get constant authentication errors for my Outlook email account. All day. Constantly. Even tried deleting the account and setting it up again. Immediately... Authentication errors. The emails do send and receive, some times, eventually. But always the constant errors. Very frustrating.
1 person found this review helpful
Mozilla Thunderbird
June 3, 2026
We're sorry you're having issues with intermittent Outlook connections, and we'd like to troubleshoot it in more detail, with help from our community. Can you please go to Settings > Get Help and open a support question with more information [and any helpful logs and screenshots]? Thank you!
Post Ghost
- Flag inappropriate
- Show review history
July 4, 2026
K-9 ran on Note 4 so many years, til update to ver. 18. caused continuous cycle of startup crashes citing: "Unfortunately, K-9 has stopped." then only a click on "Ok"possible. Uninstalled it, restarted, reinstalled, & restarted, and also updated to Ver. 19, 19.1 & 19.2. Works only after downgrade to ver. 17, but all settings & data lost. Now no poll freq. <15min. (5 was ok before). Want more stars? Explain safe upgrade -> ver. 20 (&,>). Suggested action isn't possible in android 6.0.1.
Mozilla Thunderbird
July 7, 2026
Been using Android since Gingerbread & the diversity of Android never ceases to amaze me ;-) Only have Android 8+ so can't test the following from a video on Android 6+ youtube.com/shorts/a9Z4vyOcjlo says Settings > Tap Device maintenance > Tap Battery icon>Tap OFF under "Power saving mode". Hopefully that helps
Liz Forde
- Flag inappropriate
- Show review history
June 26, 2026
Back to five stars after an issue I had with annoying folder list seems to have either disappeared or been fixed in the update I got this morning. I'm happy, app is now perfect for me, extremely happy. (Used to be a Blue Mail user, boy do they know how to completely ruin an app).
3 people found this review helpful
Mozilla Thunderbird
June 24, 2026
Can you go to Settings > General Settings > Display and see if you have the Side menu > Expand folders option? If you don't have it, or if it doesn't help, can you report this as a bug report at https://github.com/thunderbird/thunderbird-android/issues for our bug triage team and developers? Thanks!
What’s new
K-9 Mail version 20.0
New:
- Enable easily discoverable way to configure and use Thundermail
Changed:
- Only show message notification config actions above the cutoff
Fixed:
- Account drawer stayed open after account switch despite auto-select Inbox setting
- Imported settings could incorrectly show 'XX' avatar monogram
- Printed emails omitted message headers and used minimal margins
- Compose button did not work in tablet split-screen message view
New:
- Enable easily discoverable way to configure and use Thundermail
Changed:
- Only show message notification config actions above the cutoff
Fixed:
- Account drawer stayed open after account switch despite auto-select Inbox setting
- Imported settings could incorrectly show 'XX' avatar monogram
- Printed emails omitted message headers and used minimal margins
- Compose button did not work in tablet split-screen message view
App support
About the developer
MZLA TECHNOLOGIES CORPORATION
mobile-appstore-admin@thunderbird.net
447 Sutter St
San Francisco, CA 94108-4601
United States
+1 650-910-8704
