According to Gmail guide for setting up Thunderbird: ""When I delete a message," select Just mark it as deleted." I have done this, but when I delete a message the message is not 'lined through'. [It did work when I first setup the Gmail account, but has since stopped working.] When I check for email the message is removed, but it's hard to tell what messages I've deleted in my inbox before checking for new messages. Aside from this problem, everything else seems to be working properly.