Display message if user tries to send message to another user that has disabled message sending

If a user makes it to www.example.com/messages/new/UID where UID corresponds to a user that has disabled messages, no feedback alerts the user that it is impossible to send a message. The form is presented, and no suggestion is made.

I realize that in most cases, the link to the form will not appear when the receiving user has disabled messages, but in the case that they do (through a bookmark or other storage mechanism) their expectation will be to find the to field prefilled, and instead it will be blank. Further, typing in the user's name won't find it in the look ahead, because the user has turned off messaging.

A message should display alerting the user that messages are disabled.