Your new mail indicator for thunderbird is a little orange star to the left of the subject line, but within the subject area. However, any time you open a message, the little orange star disappears. It would be helpful if that orange star stayed with the unread messages for the entire day, no matter how many messages you read during that day. Then it can reset for the next day. And of course the timing would be based on local time. I would like to create a plugin that would do this, but I'm not yet adept enough to do so.