I have Thunderbird set as my default but when I use the email a file using the Send To → Mail Recipient option it only opens outlook. How do I get it to open Thunderbird.

Question

I have Thunderbird set as my default but when I use the email a file using the Send To → Mail Recipient option it only opens outlook. How do I get it to open Thunderbird.

Terri Hamilton 45

I have tried a few different solutions but none have fixed this problem. I would like to be able to send a file by clicking on it with Thunderbird as it has all my contacts, info, etc on it and I like using it better than Outlook.

Answer accepted by question author

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Answer 1

Ramesh Srinivasan 73,485 Independent Advisor

Please open Command Prompt (admin) and run this command:

reg add "HKEY_LOCAL_MACHINE\SOFTWARE\Clients\Mail" /ve /d "Mozilla Thunderbird" /f

enter image description here

Post the output.

Terri Hamilton 45 Reputation points

2026-01-23T19:37:55.6766667+00:00

It just comes back as Error: Access Denied.
Ramesh Srinivasan 73,485 Reputation points Independent Advisor

2026-01-23T19:38:38.9466667+00:00

You must run the command from Command Prompt (admin).
Terri Hamilton 45 Reputation points

2026-01-23T19:42:07.1666667+00:00

How do I get into that?
Terri Hamilton 45 Reputation points

2026-01-23T19:43:15.4533333+00:00

C:\Users\thami> This is what autopopulates
Ramesh Srinivasan 73,485 Reputation points Independent Advisor

2026-01-23T19:44:34.12+00:00

This article should help.

How to open a Windows 11 Command Prompt as Administrator

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Terri Hamilton 45 Reputation points

2026-01-23T19:55:21.5366667+00:00

ok I have done this. I am guessing there is another step because I tried to open a file and it just gave me an error. But Out look didn't open. So Progress!
Terri Hamilton 45 Reputation points

2026-01-23T23:56:51.7266667+00:00

This is what I get now.
Ramesh Srinivasan 73,485 Reputation points Independent Advisor

2026-01-24T04:14:21.02+00:00

ok I have done this.

As mentioned earlier, post the screenshot of the command you ran and the output..
Ramesh Srinivasan 73,485 Reputation points Independent Advisor

2026-01-24T04:16:41.8733333+00:00
Also, open the following folder:

C:\Program Files\WindowsApps\MozillaThunderbird.MZLA_140.7.0.0_x64__h5892qc0xkpca\VFS\Progr amFiles\MZLA Package Root

Post a screenshot of that folder.
Terri Hamilton 45 Reputation points

2026-01-24T22:36:17.9466667+00:00
Terri Hamilton 45 Reputation points

2026-01-24T22:36:49.2333333+00:00
Ramesh Srinivasan 73,485 Reputation points Independent Advisor

2026-01-25T14:26:53.82+00:00

There is a mozMapi32.dll.

But in the registry, it references mozMapi32_InUse.dll.

Changing that registry value might help.

Or, make a copy of mozMapi32.dll, and rename the copied file to mozMapi32_InUse.dll
Terri Hamilton 45 Reputation points

2026-01-25T15:13:41.96+00:00

I am unable to change the permissions so that I can modify it. I've looked on line and none of the suggestions work.

Answer 2

Ramesh Srinivasan 73,485 Independent Advisor

Hi Terri,

The Send To → Mail Recipient feature may not respect the Default Apps setting (which is per-user). Please open a Command Prompt window and run these commands to query the mail client settings.

reg query "HKEY_LOCAL_MACHINE\SOFTWARE\Clients\Mail" /s

reg query "HKEY_CURRENT_USER\SOFTWARE\Clients\Mail" /s

Copy the output to a text file and upload it in your next reply.

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Terri Hamilton 45 Reputation points

2026-01-23T19:09:26.5566667+00:00

C:\Users\thami>reg query "HKEY_CURRENT_USER\SOFTWARE\Clients\Mail" /s

ERROR: The system was unable to find the specified registry key or value.
Terri Hamilton 45 Reputation points

2026-01-23T19:11:06.27+00:00

That was for the second one. The first one it wouldn't let me post what came up.
Terri Hamilton 45 Reputation points

2026-01-23T19:13:06.48+00:00
Noticed this in all the stuff that came up.

HKEY_LOCAL_MACHINE\SOFTWARE\Clients\Mail\Microsoft Outlook\shell\open\command

(Default) REG_SZ "C:\Program Files\Microsoft Office\Root\Office16\OUTLOOK.EXE" /recycle
Ramesh Srinivasan 73,485 Reputation points Independent Advisor

2026-01-23T19:13:31.2166667+00:00

Hi Terri,

The output is difficult to read. As suggested earlier, copy them to a text file and upload it.
Terri Hamilton 45 Reputation points

2026-01-23T19:30:53.14+00:00

HKEY.pdf
Terri Hamilton 45 Reputation points

2026-01-23T19:31:20.7566667+00:00

I am hoping a PDF will work?
Ramesh Srinivasan 73,485 Reputation points Independent Advisor

2026-01-25T15:17:57.8733333+00:00
Please create a System Restore Point.

Open Regedit.exe and go to:

HKEY_LOCAL_MACHINE\SOFTWARE\Clients\Mail\Mozilla Thunderbird

Double-click DllPath

Change its data to the following:

C:\Program Files\WindowsApps\MozillaThunderbird.MZLA_140.7.0.0_x64__h5892qc0xkpca\VFS\ProgramFiles\MZLA Package Root\mozMapi32.dll
Ramesh Srinivasan 73,485 Reputation points Independent Advisor

2026-01-25T15:20:41.9666667+00:00

By the way, change only the file name, keeping the folder path intact.

Change from

mozMapi32_InUse.dll

to:

mozMapi32.dll

Answer 3

To resolve the issue of Thunderbird not opening when you use the Send To → Mail Recipient option, you need to ensure that Thunderbird is set as your default email client in the Windows settings. Here are the steps to do this:

Open the Default Programs settings:
- Go to Control Panel > Default Programs > Set your default programs.
Select Thunderbird:
- In the list of programs, find and select Thunderbird.
Set as default:
- Click on "Set this program as default" to ensure that Thunderbird is the default email client for all email-related tasks.
Check the Mailto Protocol:
- Ensure that Thunderbird is also set as the default for the mailto protocol. You can do this by selecting "Choose defaults for this program" and ensuring that the mailto option is checked.

After completing these steps, try using the Send To → Mail Recipient option again, and it should open Thunderbird instead of Outlook. If the problem persists, you may need to restart your computer to apply the changes fully.

Terri Hamilton 45 Reputation points

2026-01-23T17:50:54.6033333+00:00

Thunderbird is already set as my default. But I haven't been able to either uninstall Outlook completely or unset it as default for some items either.

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I have Thunderbird set as my default but when I use the email a file using the Send To → Mail Recipient option it only opens outlook. How do I get it to open Thunderbird.

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