I have the message system enabled on jobs and experts.
When a message is sent via the inbox > compose feature the email triggered has a broken link...
"[username shows here] has sent you a message on [site name shows here]
[message shows here]
Check your messages here /demo/wp-admin/admin-ajax.php?message_id=451 "
(In this URL partial URL example demo is the name of the multisite this has come from.)
This was triggered by sending a message between users on http://twid.simplecsr.com/demo/