Case creation error question

Case creation error question

Hello, 
I have a question about the case creation rule. We have internal users who have CRM support issues, and we wasnt to manage that in CRM through Cases. I have a workflow setup to create cases from the support queue, and send an automatic reply. Internal users may or may not be users in CRM(New hires etc.). I want a case created and the reply mail sent to everyone who sends a mail to the support mail account. I am having trouble selecting the the contact/user record to send the mail to as some are users and others contacts. How can i select the send to on the email so that the workflow does not fail?
am new to the here, I have worked with multiple firms. you can check Information security video one of my work.

Thank you !