Here is a picture showing the issue.

Regards

What happens if you check the box 'Always use this app to open jpg files'?

Are you serious ? Do you really think I haven't tried ?

Alkerion said

Are you serious ? Do you really think I haven't tried ?

Well he is not the only one to wonder..... Of cource the other option is the email is malformed. the action in Thunderbird is for mime type "image/jpg" is that mime type specified in the image source? (Ctrl+U).

What I see usually is rubbish type encodings with things like application/octet stream used by developers that simply do not understand what they are doing.

Hi,

The mime is: Content-Type: image/jpeg; name="222713.jpg"

The exact same mime is displayed in Tools/Options/Attachments under JPG images.

Even mails sent with TB containing .jpg attachment poses the issue...

I've tried to open TB as Admin, no change, keep asking.

When I open a JPG file from Explorer there is no issue, Irfan open the image as expected.

Only facing this issue with JPG, no otehr file type behave like that and opens directly.

I finally "solved" the issue by doing this:

Run / gpedit.msc (edit group policy)

locate and expand Computer Configuration / Administrative Templates / Windows Components now click on File Explorer on the right panel, double click on "Do not show the 'new application installed' notification" and set it to "Enabled"

That seems like a odd workaround that might have other effects. I would hope this could be reported as a bug and worked on by the Tbird team.

I left it alone, but the issue is clearly a windows one.

If attachments in Thunderbird are correctly showing the appropriate application, although I do think you should remove the setting and allow it to be recreated to make sure it is correct. The only other option is windows has a problem with file associations for the file type.