I promise I searched and read messages, but could not understand how threading works in Thunderbird. With respect to all the other apps I use, I consider threading in Thunderbird unusable. - New emails assigned to a thread, do not clearly show on top of the list (depending on the sort criteria of the mailbox/folder). - Sometimes, emails get grouped in the same thread even if they have a different subject. I assume Thuderbird uses fields different to the email subject, but there should be a way not to automtically group messages whose subject is different. Is there a link to a documentation page that helps in making sense of threading?