When a user's PM box becomes 100% full (500 messages), what happens?

If someone tries to send a PM to that user, are they notified of the full mailbox? (I would hope so but I've never received such a notification from FT.) Before or after composing the message? I.e., only when hitting send or when the username is entered as a recipient of the message?

If the notification comes at the "send" step, is the message retained as a draft that can easily be sent later by just hitting send? Or does the message go into a queue to be sent when there is space in the inbox or attempted at regular intervals? Or (bad) is the attempted message simply lost?

When space is created in the mailbox, are the previously attempted incoming messages resent (if the completed messages were retained in a queue) and if so, how quickly and in what order (FIFO or LIFO)? Do people who attempted to send messages when the mailbox was full receive a notification? Would they receive a notification later that the message had automatically been successfully sent?