What Mozilla needs

I may have totally missed where this feature is, but what Mozilla really needs is a place where you can go and cancel/delete your unsent messages. Right now, when I queue emails to be sent later, if for some reason they fail or I change my mind, I have no recourse to delete them. Either they all fail or they all go. As a result, I've sent some emails I didn't mean to -- for whatever reason -- and I also have emails queued up in my 'send later' folder that I no longer need to send later because I've already sent them. In theory, these 'unsent letters' should end up in the local folders, but that doesn't always happen (I don't know why). In the past, I think I've gotten around this problem by actually going into the program files and deleting out the unsent mail file; however, there has to be an easier, less techy way of dong this. Help?