I have version 140.1.1esr and the delete button does behave like always : it deletes the email not the attachment.

I have that same version and yes it does delete the email but only if that was the last thing selected. If the last thing I do is click the attachment (to save it) the Delete button would then delete the attachment, unless I first click back onto the message rather than the attachment.

It never used to work like this. Previously I could save the attachment and then click the button to delete the message and that's what it then did.

Hey, look at us, three Michael's working together on this.

I am curious about this one but I am unable to reproduce this on my machine. When I try to do this, the email deletes, as would be expected. Not to imply your post was not descriptive, but in order to assist better could you provide me with details steps to reproduce.

(Example: 1. I clicked on an email with this attachment type, 2. then I clicked (here) to save the file to my desktop. Then I clicked here next, etc.)

This will help me troubleshoot from my end.

Also, just to be safe, try to test the behavior with Thunderbird in Troubleshoot mode to see if an addon is causing the issue (Menu -> HELP -> Troubleshoot Mode)

OK so I ran the program in troubleshoot mode as suggested.

I selected a message from the list by clicking it. Note a single click so the messages appears below the list of messages not in it's own window/tab.

I right clicked the attachment and selected 'Save' and saved to file. This effectively selected the attachment so it was highlighted in blue.

I then clicked the Delete button (just above the message and below the list of messages).

I then got the warning about permanently deleting the attachment.

If I first click back into the message so the attachment is no longer selected then it works normally. But I did not need to do this before. I have attached a screen shot where you can see the selected attachment and the warning message.

Edit to add: Actually the saving is irrelevant; you can just left click the attachment and do nothing with it and then just go ahead and click the "Delete this message" button and it tries to delete the attachment.

See attachment in later post

OK here's another screenshot with the sequence shown on it exactly as I do it; just the three clicks. Hopefully that makes it very clear!

Suggestion : delete your uploaded screen shot because it contains private information. Maybe you should masked all private information before re-upload.

Thanks for adding more information - it's important to know WHICH delete button you are using.

I've never seen a report of this before, only use of the delete KEY - perhaps one is listed in https://mzl.la/3UvNlqo