Message Filters only run automatically on the Inbox.

Message Filters only run on other folders by manual input.

However, you may find the following method less frustrating and easier. If you select the BulkMail folder in Folder Pane first and then open Message Filters, you will find 'BulkMail on mail account' is auto entered in the 'Run selected filter's on'.

First-of-all, many thanks. At least I now know that there's no way to get message filters to run automatically on any folders other than the Inbox. It's a pity that this rigidity is built-in to Thunderbird but perhaps it's there to avoid infinite loops or other catastrophes. Secondly, the tip that one can select BulkMail in the Folder Pane is welcome but not really helpful. In a way it's like telling me that if I need to push my car to the gas station, to make it easier I should release the emrgency brake . . . Anyhow, many thanks!

In a way it's like telling me that if I need to push my car to the gas station, to make it easier I should release the emrgency brake . . . Anyhow, many thanks!

You might be surprised how many people do not know how to do that, or press Ctrl+A to select all or even close the colour wheel when they are done so their selection updates to Thunderbird.

We find assuming you know nothing less frustrating that assuming you have some knowledge and then spending 10 messages back and forth explaining how to take a screen capture or post an image that is not in word DOCX format. We get accused of being patronizing but unfortunately all people are not created equal, much as we would like them to be.

Good point! I should not have been so quick to brush aside Toad-Hall's tip. Yes, one can easily over-estimate the knowhow of users. When I was using IBM mainframe computers in the late 1960s, a common refrain was "the computer made a mistake". (Admittedly I am not a teenager.) And today when I hear "my phone is broken", it usually means that a setting has been inadvertently changed. Keep up the good work!