I have a website application that needs to send email via our Exchange servers. It sends email internally fine, but when sending to an external address I get the 550 5.7.1 unable to relay error. I followed this guide to create a connector to allow relay. Unfortunately, all office email was trying to use that connector and was not being routed correctly. It also appeared as though it opened it up for spammers to use. This is obviously unacceptable and a secure method is needed.