Filtering occurs only on the message headers.

I guess you could use the x-mozilla.status header and set it to unread. There used to be some blog posts on the web that decoded the values used. My understanding of the new and unseen status that is used to place the marks against folders and mail being shown for the first time is that it is not stored in the message header, so would be unavailable for a filter.

See the attached picture.

Thank you for the picture. New did not appear with my TB, but now it does. Actually, I would like to do the following:

Copy newly arrived messages from one of my IMAP account to my local folder. But using New runs the risk of repeat copies. So, is there a way to apply the filter only once. I thought of marking the original messages as Read but the filter applies this before the copying !

Any other solutions ?

At this point, I keep on applying the Remove duplicate command on my local folder, but if I delete or move one of those recently copied messages, the original gets copied again (something I do not want to happen!)

Thanks for any help.

Thanks for any help.

If a filter runs when getting new messages, in principle, a message can only be 'new' once, i.e. when it is first downloaded. So, a filter that acts on new messages should only perform the action once, and I don't know why messages that have been copied to Local Folders would be copied again after the LF copies are moved or deleted.