I suggest you close thunderbird and log into your gmail account online. There you can see if it is Gmail marking the messages junk and not Thunderbird. I also use Gmail and often find that is the cause. If you determine that Gmail is not doing it, then I suggest a review of the spam filtering features of thunderbird here: https://blog.thunderbird.net/2024/09/thunderbird-and-spam/ For the second junk filter, I suggest first determining which one is being used and then see if you can rightclick and delete the other.

Thank you david for your speedy, helpful response. I'll do as you say and see if it solves the problem one way or another. I just thought it was strange that it's never been a problem before in all the years I've been using it (I'm 73 and only a little computer literate!) and now it suddenly is.

Thanks, once again. Mark

david, I've got no mail in either of the Junk folders how do I know which one is active, please?

My approach is to mark something junk and then see where it goes. Not high-tech, but I tend to just blunder ahead and see what happens. I'm glad to assist. :)

Thanks again, david. I'll try that. Mark

It turns out that Gmail has two folders (or tags) for undesirable email: one for Spam and one for Bulk. So, each Gmail account will have two folders in the TB Junk folder. There is no way in the Accounts setup to determine which one is to be used. John

Thank you, John. I'll take a closer look when I get a chance. Mark