Finished the GMS setup and ready to do the over-the-air installation, but in the server log it shows "Error Sending SMTP Message: '550 5.7.1 Unable to relay for'

Does GMS have it's own built in SMTP engine or is using someone elses or my GWIA? I don't see anything on the GWIA when trying to submit and the error is immediate. I've put in exceptions in my GWIA for this machine to be able to relay but didn't help.