I have a queue set up and within that queue I have an automatic record creation rule which basically converts emails that come into the queue into cases. The customer then gets an auto response back with a case number. 

I thought that if the customer replies to that auto response number it would add the email as a post on the case however, instead it creates a separate case. 

Is there anyway to make it so that if the customer replies with the same case reference number in the subject it would add it to the existing case rather than create a new case?

Many thanks for your help in advance.