Mail folder question

[perzaklie]

Sometimes I see a folder in the left hand preview panel that will be bolded and have a number beside it. I open the folder and see messages in bold that I don't know how they got into the folder. If I right click on the folder, I get a popup menu. One of the options is Mark Folder Read. I select this option and the color does not change, it stays black. Am I missing something?

[DanRaisch]

How is the account set up in Thunderbird, as POP or IMAP? Find out using menu path Tools->Account Settings->Server Settings->Server Type at the top right of the dialogue.
Do you regularly compact the message folders?
If not, in the right click context menu, select "Properties" then click on the "Repair Folder" button when it is displayed.