This setting affects your LOCAL HELO settings without you having to create a custom SMTP banner or change the host name of the Nethsrever install. I was confused at first being that it was in the Relay section but this was incorrect on my part. The picture above that has the WHAT.the.fudge HELO response after I changed the Custom HELO message to WHAT.the.fudge and would be the solution you were looking for without needing the custom SMTP banner changes that Andy suggested.