Email Loop

Hi,

Exchange 2010

Ive started to see an issue where a customers out of office hits one of my mailboxes (which has an autoresponder email)  and then starts to get into a loop.

There are thousands upon thousands of emails coming in from the same external email and the same subject line of "Automatische Antwort: Automatic reply: Automatische Antwort: Automatic reply:"

At the moment Ive created a transport rule to delete these when they come in, but how do I resolve this long term?

Any ideas would be greatful