I don't even see the Email heading. Go to TB menu > Settings > General > System Integration. Is 'Always check to see if Thunderbird is the default mail client on startup' enabled? Even if it is, click the 'Check now' button, then the 'Set as default' button'.

Thank you, Ed! I've done all that before posting my question. Everything is OK with 'mailto'. However, what I want is something different: when I decide to SHARE something by MAIL (an image for example) and I click on the appropriate button, I get a single choice for MAIL: Outlook (which I don't use). How can I modify things so that I get also (or only) Thunderbird as a choice? Thanks a lot! Robi

Aha! Send to Mail recipient only lists Windows apps. Instead, add a 'Send to' shortcut for Thunderbird following the instructions at https://www.pcmag.com/how-to/how-to-customize-the-send-to-menu-in-windows.

I just replied with the probable solution, but it has a flagged link so it may take a bit to get approved.

Thank you, Ed! But what I wanted is a trick to get Thunderbird offered in the SHARE procedure. If that is impossible, well never mind! All the best, Robi

It is not possible, but doesn't 'Send to' Thunderbird have the same result? Maybe I'm not up to date on what Share does.

Yes, 'Send to' Thunderbird has the same result, but it isn't fair that SHARE cannot include Thunderbird, since it includes, e.g., Whatsapp.

Thank you, Ed! But what I wanted is a trick to get Thunderbird offered in the SHARE procedure. If that is impossible, well never mind! All the best, Robi

Try installing it from the windows store. I have not tried it, but the manfist required is fairly routine for app store programs. I just do not know It the Thunderbird package contains on or not, so you will have to try it. I would honestly be interested in the answer though as this sounds like a bug worthy issue either way.

Thanks, Matt! I followed your advice. I uninstalled Thunderbird, restarted the system and then installed Thunderbird from the Windows Store: Thunderbird Windows MSIX packagethunderbird-MSIX - 1.0 But for emails the Share window still offers only Outlook. All the best, Robi

From what I understand, an app needs to be registered as a share target for it to appear in Share. Apparently, TB doesn't have that registration.

Hi Matt, Hi Ed! The "bug" also occurs under Win 10. Best, Robi

Have you got the following selected in Registry Editor ? see image below

Thank you, Toad-Hall, for your perfect instructions! Yes, TB appears in Registry Editor exactly as you show. I suspect that Ed is right when he writes that TB doesn't have the appropriate registration as a Share target. All the best, Robi

Here are the steps for registering a non-windows app as a share target.

The 'steps' advice is not designed for use by users. The information is for developers of their own app.

The following info I found posted by a Microsoft Agent/ Moderator in a microsoft support forum.

Windows 11 does not currently allow users to manually add non-Microsoft Store apps like Thunderbird to the Share menu. Only apps that are integrated with the Windows Share contract (typically Microsoft Store apps) will appear in the Share panel

While Thunderbird can't be added directly to the Share menu, here are a couple of alternatives: Use "Send to > Mail recipient": Right-click a file in File Explorer. Choose Send to > Mail recipient. If Thunderbird is set as your default mail app, it should open a new message with the file attached.

Now, recently Thunderbird has been added to the 'Microsoft Store Apps', but whether that installation works via Share is another matter as I've not tested it. Not everyone wants to use the Microsoft Store App version for various reasons, one reason being it uses it's own different location for storing Thunderbird profiles which is not exactly that convenience nor as easy to find.

This is basically Microsoft causing the problem.

OP already installed TB from the MS store on Matt's advice and said it didn't work.

OP also said Send to has the same result but "it isn't fair that SHARE cannot include Thunderbird, since it includes, e.g., Whatsapp."

Is it worth filing a bug for adding share target registration to the Win version?

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BTW, the Microsoft Agent/ Moderator's instructions for using 'Send to' includes

"If Thunderbird is set as your default mail app, it should open a new message with the file attached."

I have not found TB listed under 'Send to' on any Win version; I've always had to add it using the method I described above (https://support.mozilla.org/en-US/questions/1516000#answer-1740714).

I confirm that I installed TB from the MS store on Matt's advice, but it didn't work. I then uninstalled MS Store TB (not so user-friendly as Mozilla’s) and re-installed the original. I never had problems with ‘Send to’ under Win 11, but I do hope that you will file a bug ‘for adding share target registration to the Win version’. I’m grateful to you all, Robi.