Paul Coghlan wrote :
I had assumed it would be a Special page but have no place to start from.
Is there something similar in existence I can look at as far as you know?
Yes, there is already an e-mail form implemented in mediawiki, however, it only allows user-to-user mailing. But you can easily modify the php code it to allow anonymous mailing and create an extension on this.
See : /includes/SpecialEmailuser.php