Thunderbird 91.4.0

[German]The developers of the Thunderbird email client have released Thunderbird 91.4.0 on December 7, 2021. This is a maintenance update for the 91 development branch, which makes numerous fixes. Here's a brief overview. TB 91.4.0 (portable) breaks my system.


German blog reader Tom pointed it out here – thanks for that. According to the release notes, the update includes the following fixes. Some fixes might address the slow startup of previous Thunderbird versions, also discussed here on the blog.

  • Improved IMAP startup performance for accounts with a large number of folders
  • Thunderbird could not send messages when an IPv6 SMTP server was configured by IP address (instead of hostname)
  • Forwarding messages with attachments sometimes failed
  • Printing multiple messages at once was not possible
  • Non-utf8 newsgroups were not supported
  • Thunderbird got stuck after sending a message with NNTP and SMTP recipients
  • Using Thunderbird with multiple language packages caused high RAM and CPU usage and sluggish performance
  • Clicking on a "mailto:" launched Composer with the default sending identity instead of a configured alternate identity
  • Dragging and dropping text into a plain text message in the Composer window was handled inconsistently
  • FileLink messages were not displayed correctly when viewed in Outlook
  • When setting up an account, it was not possible to create an IMAP/POP account after selecting a protocol with an extension
  • Multiday selections were not deleted when changing the displayed week
  • When creating a new event by clicking and dragging the mouse to create a field, the view did not automatically scroll when the end was reached
  • The calendar invitation field did not scroll when multiple invitations were pending
  • The calendar print dialog did not have a cancel button

In addition, some security fixes that were rated as high were made. Warnung: After upgrading to TB 91.4.0 portable on my Windows 7 SP1 ESU, the mail client shows an empty window.

Leerer Thunderbird

I installed an older portable version, and then I got my old content back.

System requirements

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


  • Windows: Windows 7  or higher
  • Mac: Mac OS X 10.9  or higher
  • Linux: GTK+ 3.14  or higher

The download of the free Thunderbird is available here.

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