Generally it is caused by receiving the mail on another device. IMAP stores the read unread status on the server, not locally. This results in Thunderbird settings being ignored for mail that the server is already of the opinion is read.

My guess is historically you used a POP mail protocol to get mail in Thunderbird and stumbled upon it again by switching to a 32bit version. It is presented as an option for most mail providers, but you have to know to select it and most folk just select the default (IMAP)

Thanks for the answer, so you suggest to use pop mail protocol if I understand you correctly?

Hi, just upgrade to Windows1 and did a new installation from Thunderbird. latest version 115.11.0 (32-bits) 1. But the new messages are almost directly market as read even with setting mark messages automatic as read set to no? 2. On a other pc with Windows11 I had the same problem with the 64bit version but going to the 32bit version solved the problem. Any Idea how to solved this problem? Regards Karina

To me, neither of these two statements make sense.

1. 1 - the default download offered by the Thunderbird website to Windows users is 64bit, unless you are running Windows in 32bit mode which you most certainly are not doing with Windows 11.

1. 2 There is functionally no difference between 32 and 64bit Thunderbird, so some aspect related to you reinstalling caused a changed - it wasn't a "difference" between 32 v 64 Thunderbird code.

Perhaps try starting Thunderbird in Troubleshoot Mode, and change back to normal mode.

Generally it is caused by receiving the mail on another device. IMAP stores the read unread status on the server, not locally. This results in Thunderbird settings being ignored for mail that the server is already of the opinion is read.

That solved the problem, Change to POP3 and now it is working as expected. Also upgrade to 64bit and it is still working.

Thanks for the help.