Workflow Email to Case for CRM 2011 on-premise

Senario is :

using CRM 2011 on-premise+CRM for outlook2010 installed.

- Support Q created in CRM with admin user, to receive customer mails to help them to solve their inquires ,

IF Email To equal Support Q. done

Create Case .                         done

send email to customer ,        done

all above works fine               done

But

I want to stop conversion if the email To: filed has the support email and another recipients.

what if condition should I use ?

then send email rejection to the customer done

stop workflow succeed or cancel ?

Regards