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K-9 Mail

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K-9 Mail
Original author(s)Jesse Vincent
Developer(s)MZLA Technologies Corporation, Christian Ketterer
Stable release
6.803 / 10 May 2024; 36 days ago (10 May 2024)
Written inJava, Kotlin
Operating systemAndroid
TypeEmail application
LicenseApache License 2.0

K-9 Mail is free and open source email client for Android. It is designed as an alternative to the stock email clients included with the platform; it supports both POP3 and IMAP protocols and supports IMAP IDLE for real-time notifications. The project is named after the Doctor Who character K9.[citation needed][1]

Previous logo


The source code was first published to its git repository on October 27, 2008[2] by Jesse Vincent and the first binaries were released to the public on the Google Code site the same month.[3]

In 2015 the project received $86,000 of funding from the Open Technology Fund.[4]

On 13 June 2022, it was announced that K-9 Mail had been taken over by MZLA Technologies Corporation, a subsidiary of the Mozilla Foundation with current maintainer Christian Ketterer joining the team, and plans for K-9 Mail to be rebranded as Thunderbird for Android following the completion of a feature roadmap, including sync with Thunderbird on PC, integrating Thunderbird's automated account setup system, message filtering, and improvements to folders.[5]


This application has been downloaded from the Google Play Store between 5 million and 10 million times since its release and has been rated by over 90,000 people with almost as many 1 star reviews as 5 star reviews many due to the fundamental restructuring of the program in August 2021, which was not widely accepted by the user base and more recently because of the battery usage when using push to fetch mail.

In the early 2010s it was widely reviewed, and was particularly praised in the media between 2011 and 2013 as a replacement for the default mail application.[6][7] At the time, it was a leading alternative Android app, often recommended[8] when a user did not want to use the default app. It was awarded the "Best App for Sending Email" in the 2010 "Best Android Apps" book.[9]


  • Works with IMAP, POP3
  • Folder Sync
  • Encryption with OpenKeychain support
  • Signatures
  • SD Card Storage

See also[edit]


  1. ^ "About". Retrieved 1 February 2024.
  2. ^ "k9mail/k-9". Github. Retrieved 1 September 2013.
  3. ^ "Downloads - k9mail - K-9 Mail is an advanced email client for Android - Google Project Hosting". Retrieved 2013-08-15.
  4. ^ Open Technology Fund. "Projects we support - K-9 Mail". Open Technology Fund Website. U.S. Agency for Global Media. Retrieved 2022-03-13.
  5. ^ Axon, Samuel (2022-06-13). "Email client K-9 Mail will become Thunderbird for Android". Ars Technica. Retrieved 2022-06-14.
  6. ^ Paul, Ryan (2011-01-24). "Excellent K-9 mail app for Android keeps your messages on a leash". Ars Technica. Retrieved 2013-08-15.
  7. ^ "K-9 Mail Receives First Significant Update In 9 Months - Improved Interface, Altered Widget, Bug Fixes, And More". Androidpolice.com. 2013-06-28. Retrieved 2013-08-15.
  8. ^ Begun, Daniel (2011). Amazing Android Apps for Dummies. Wiley. ISBN 9781118061428.
  9. ^ Hendrickson, Mike (2010). Best Android Apps. O'Reilly Media. p. 80. ISBN 9781449382551.

External links[edit]