Thunderbird 91.4.0 Email Client has been released

Martin Brinkmann
Dec 8, 2021

The developers of the open source email client Thunderbird have released Thunderbird 91.4.0 for all supported operating systems.

The new version of Thunderbird is a bug fix and security update. Thunderbird installations should receive the update automatically through the built-in automatic updating system. Users who don't want to wait for that to happen can run a manual update by selecting Help > About Thunderbird from the main menu. If the main menu is not displayed, tap on the Alt-key on the keyboard to display it.

Thunderbird queries the organization's servers to find out if a new update is available. If found, the update will be downloaded and installed.

Thunderbird 91.4.0

Thunderbird 91.4.0 improves the performance of the email client in several scenarios. Installations with "a multitude of folders" will see improved startup performance after the installation of the new version.

Thunderbird installations with multiple language packs will also see improvements, as the engineers fixed an issue that caused high RAM and CPU usage resulting in a "sluggish performance".

Here is the remaining list of changes in the new version of Thunderbird:

  • Thunderbird failed to send messages when an IP address was configured as an IPv6 SMTP server (and not a hostname).
  • Fixed an issue that caused the forwarding of messages with attachments to fail sometimes.
  • Multiple messages printing works now.
  • Added support for non-UTF8 news groups.
  • Fixed an issue that caused Thunderbird to stall after sending messages with NNTP and SMTP recipients.
  • Activating mailto links caused the composer to start with the default sending identity instead of a "configured alternative".
  • Fixed a plain text message drag & drop issue.
  • Outlook did not display FileLink messages correctly.
  • After selecting an extension provided protocol, it was no longer possible to create an IMAP/POP account.
  • Thunderbird's calendar did not clear multiday selections when changing the viewed week.
  • The view of a new event did not autoscroll after reaching the bottom when creating a new event by "clicking and dragging the mouse to create a box".
  • The Calendar invitation panel did not scroll when multiple invitations were pending.
  • The Calendar print dialog lacked a cancel button.

Thunderbird 91.4.0 addresses several security issues. The highest severity rating is high, the second-highest after critical.

Here is the list of fixed issues:

  • CVE-2021-43536: URL leakage when navigating while executing asynchronous function
  • CVE-2021-43537: Heap buffer overflow when using structured clone
  • CVE-2021-43538: Missing fullscreen and pointer lock notification when requesting both
  • CVE-2021-43539: GC rooting failure when calling wasm instance methods
  • CVE-2021-43541: External protocol handler parameters were unescaped
  • CVE-2021-43542: XMLHttpRequest error codes could have leaked the existence of an external protocol handler
  • CVE-2021-43543: Bypass of CSP sandbox directive when embedding
  • CVE-2021-43545: Denial of Service when using the Location API in a loop
  • CVE-2021-43546: Cursor spoofing could overlay user interface when native cursor is zoomed
  • CVE-2021-43528: JavaScript unexpectedly enabled for the composition area
  • MOZ-2021-0009: Memory safety bugs fixed in Thunderbird 91.4.0

Now You: which email client do you use?

Thunderbird 91.4.0 Email Client has been released
Article Name
Thunderbird 91.4.0 Email Client has been released
The developers of the open source email client Thunderbird have released Thunderbird 91.4.0 for all supported operating systems.
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  1. Lindsey said on December 10, 2021 at 10:56 pm

    This recent update shut everything down so I cannot access any of my email accounts. I’m not impressed and I’ve gone through all the trouble shooting. I’ve used this program for many years but it may be time to move on.

    1. Wayne said on December 20, 2021 at 6:48 pm

      > This recent update shut everything down so I cannot access any of my email accounts

      @lindsey, and no resolution after asking in ?

  2. solano said on December 10, 2021 at 12:09 am

    A partir da versão 91 o Thunderbitd ficou muito ruim. “Come” a última linha dos anexos TXT e nas respostas, copia todas as linhas e coloca os anexos no corpo do e-mail. Muito ruim.

  3. semce2 said on December 9, 2021 at 1:35 pm

    Multi-Xpunge still working for me Maybe you need a newer version of Multi-Xpunge. Be sure you have your clients configured. I also have a ProtonMail account for more private email. Both are working well for me.

  4. Dimitri said on December 9, 2021 at 11:48 am

    Evolution on Linux is simply superb and honestly superior to TB in every way, especially compatibility with various mail servers (inlc. Exchange) and better compliance with IMAP.

    But the main advantage that TB has is that it’s cross platform and that makes it the only game in town.

  5. Greg said on December 9, 2021 at 6:09 am

    expect a 91.4.1 anytime

    1. Wayne said on December 20, 2021 at 6:46 pm

      > expect a 91.4.1 anytime

      shipped this morning

  6. El Narizon said on December 8, 2021 at 9:07 pm

    With Thunderbird 91.4.0 several addons stopped working, like for example Mail Merge or Xpunge.

    Mail Merge: the menu entry is gone
    Xpunge:icon is still there, clicking it does nothing

    I don’t know how much more addons are affected, I assume a lot.

    1. Wayne said on December 9, 2021 at 11:31 am
      1. JoSi said on December 16, 2021 at 8:53 pm

        Thanks! They should promote that more.

  7. Paul(us) said on December 8, 2021 at 7:22 pm

    Loving Thunderbird. And not only because of the add-on adding possibility.
    Hopefully there will come more add-ons in the foreseeable feature.

    Thunderbird Is not as easy as outlook 2019 to handle.
    But its much more than good enough and hopefully Mozilla Thunderbird implementing, especially more work flow function (After security updates.). Then Thunderbird will become the absolute number one.

  8. walker said on December 8, 2021 at 5:31 pm

    >which email client do you use?

  9. ULBoom said on December 8, 2021 at 4:11 pm

    Thunderbird on desktop, Fairmail for mobile.

    I’ve tried every (that I know of) client appropriate to our simple email needs that isn’t designed for kids and haven’t found anything as good as TBird. Some are ancient versions of TBird with options removed, weird. Thunderbird was flaky during the transition back to Mozilla but seems solid now.

    If Fairmail had a desktop version, I might use that, it’s great for mobile. I’ve donated to both clients, no problem for stuff that works well. Both have a multitude of privacy and anti-tracking settings.

    I run three different mail services through both, no problems.

  10. Anonymous said on December 8, 2021 at 1:38 pm

    I use Thunderbird for some email, also use it as a news reader.

  11. m3city said on December 8, 2021 at 11:43 am

    I use Thunderbird. Used Fossamail by Moonchild.

    Just last week I tried The Bat, considering a paid version ~50E. And I was amazed how fast it is, used one fifth of TB memory, how customizable it is. It is all good BUT what bothers me is that I would have to pay for an update. Right, less than a full licence but still too much – 30E. I looked through version history and it doest look like generational changes occured, but rather ordinary bug fixes and some features added. That does not mandate such high upgrade price for me.

    And there is ClawsMail, that is equally lightweight/powerfull as Ritlabs’ soft, but I think it’s a little bit stuck in the past. A plugin just to show message in html, need to manually click it every time? Oh, come on.

    I like TB for the extensions, ability to connect calendar and tasks to my nextcloud server, but I have to admit it is bloated and fat. I just cant get it why TheBat occupies 50MB in memory and starts up instantly, and TB… well, it starts. One can hope that JMAP may land in TB faster than anywhere else.

    And thats my 2 cents about e-mail software. Anyone has a tip, “success or failure” story with another program?

    1. ULBoom said on December 8, 2021 at 4:29 pm

      I really wanted Claws to work, I’ve tried it a few times, even in different compatibility modes, which broke it more than it already was. Valiant effort but just too glitchy in most respects. The ancient interface doesn’t matter to me, it wouldn’t download or send consistently, images sometimes loaded or not, lots of problems.

      Seamonkey has a mail client. Also a browser, office, others. The browser works fine, ancient appearance though. Try their email client if you’re an experimenter. Seamonkey is definitely an unusual suite of stuff and it’s kept up to date fairly well.

      1. Ray said on December 10, 2021 at 12:48 am

        Seamonkey is basically in maintenance mode. There are only about five (or less) active developers. Most of the time, they are playing catch up with porting back security patches from newer versions of Firefox and Thunderbird.

        Would like to see some competition in the email client space. Whatever happened to Vivaldi’s integrated mail client? Mailbird and Mailspring look promising, but both clients have premium features locked behind a paywall. Mallspring is also powered by Electron, which is bloated. BlueMail is another option as well. I’ve just given Ghacks some ideas for more blog articles :)

      2. m3city said on December 9, 2021 at 9:07 am

        Thanks. Seamonkey brings my attention from time to time. Outdated is a good word here. But actually I’ve never tried it’s mail client, assuming it’s just some version of thunderbird. If seamonkey team had capacity to switch internals to current FF, and mail client was equal to TB… I would search no more.

  12. ilev said on December 8, 2021 at 9:05 am

    I use Gmail. No bugs, mail sent and received flawlessly.
    The best spam filters in the industry.

    1. Wayne Gifford said on December 10, 2021 at 4:05 am

      I use Gmail for it’s both mail and spam filters, but read and file my mail with Thunderbird. I love IMAP

    2. G.o.a.t.mail said on December 8, 2021 at 10:57 am

      Plus the best tracking, monitoring and data collection of all industries.

      1. Sundar said on December 8, 2021 at 7:39 pm


        Who cares? It doesn’t matter in real life. All this tracking-monitoring verbiage is mostly a marketing scam to pull budgets from advertisers. Just install an adblocker and forget about them and your tinfoil hat.

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