I've started having a strange problem with Leopard Mail. When I first open it, it will receive all my incoming mail without issue, but once it's open it will not receive at all. I have to quit and reopen it to receive any more messages. It's not giving me any error messages at all - when I hit the receive button, I simply see not actions being taken in the Mail Activity pane at all.
Does anyone have an idea on fixing this?