K-9 Mail

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K-9 Mail
Original author(s)Jesse Vincent
Developer(s)MZLA Technologies Corporation, Christian Ketterer
Stable release
6.202 / 26 July 2022; 2 months ago (26 July 2022)
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.

In 2015 the project received $86,000 of funding from the Open Technology Fund.[1]

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.[2]


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 unacceptable battery usage when using push to fetch mail. It has been widely reviewed, and was particularly praised in the media between 2011 and 2013 as a replacement for the default mail application.[3][4]


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

Missing features[edit]

  • The application does not allow viewing the sender name and sender e-mail address at the same time when viewing an e-mail. Its either display the sender name or display the sender e-mail address.
  • The application does not allow text mode reading of e-mails, meaning web content in e-mails will render, posing a security risk.
  • The application does not allow the viewing of e-mail source code.
  • The application does not allow composing an e-mail mono-spaced font, which makes it difficult to include Ascii Art or just simply align items in a list.[5]
  • The application does not allow switching off automatically opening HTML attachments, which might expose the user to phishing.[6]

See also[edit]


  1. ^ Open Technology Fund. "Projects we support - K-9 Mail". Open Technology Fund Website. U.S. Agency for Global Media. Retrieved 2022-03-13.
  2. ^ Axon, Samuel (2022-06-13). "Email client K-9 Mail will become Thunderbird for Android". Ars Technica. Retrieved 2022-06-14.
  3. ^ Paul, Ryan (2011-01-24). "Excellent K-9 mail app for Android keeps your messages on a leash". Ars Technica. Retrieved 2013-08-15.
  4. ^ "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.
  5. ^ "Add option to use fixed-width font when composing messages".
  6. ^ "Add option for default display format".

External links[edit]