I got an e-mail yesterday evening:
However, I had completely emptied it days before. Right now it says:[Username] has just tried to send you a private message. However, your private messages box on FSUniverse has reached the specified quota. In order to receive further private messages, you must delete some messages.
Edit: Oddly, I was then able to send a PM myself.Inbox contains 2 messages. You have 4 messages stored, of a total 30 allowed.