Thunderbird 91.3.0

[German]The developers of the Thunderbird email client have released Thunderbird 91.3.0 on November 3, 2021. This is a maintenance and security update for the 91 development branch, which makes minor fixes. In particular, a number of vulnerabilities rated as high have been fixed. However, the signature problem with Microsoft Outlook still exists. Here's a brief overview.


Tom has pointed out the update in this comment (thanks for that). According to the release notes, the update includes the following fixes.

  • Default mail headers were set incorrectly when the value contained a colon (:)
  • Thunderbird did not send the QUIT command when closing an SMTP connection
  • Mail tabs could not be closed using the context menu
  • "Print" context menu was still shown when no message pane was displayed
  • Windows tray icon did not reappear after restarting Windows Explorer
  • Compose window attachment drag and drop fixes
  • Various macOS stability improvements
  • Drag and Drop area for file attachments on Windows was incorrect
  • CardDAV address books without a name did not work
  • Thunderbird tried to refresh disabled and manual-only calendars when the network state changed from offline to online
  • Various Calendar event dialog fixes

According to this page, various security fixes, some rated as high (use-after-free vulnerability in the file picker dialog, etc.), others as moderate, have also been made. The mail client should therefore be updated quickly.  

In the blog post Thunderbird 78.x: Upgrade to version 91, and foreseeable problems I had pointed out a signature problem with Outlook. According to this comment, the bug is still present in 91.3.0. I have had also an install error writing to tmp folder – but the update is reported as successful.

System requirements

The system requirements for the different operating system versions (see here for more details):

  • Windows: Windows 7, Windows Server 2008 R2 or higher
  • Mac: Mac OS X 10.12 or higher (macOS 11.0 for Silicon)
  • Linux: GTK+ 3.14 or higher

The download of the free Thunderbird is available here.

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