Email Alert Failure on WSUS server

I have a WSUS server set up and working. I keep getting errors however saying that Email Notifications are failing.

When I attempt to test the emailing capabilities of the WSUS server I receive an error saying:

System.Net.Mail.SmtpException: Syntax error, command unrecognized. The server response was: Your IP x.x.x.x does not have a reverse DNS entry. Diconnecting…

I have verified that the server does, in fact, have a PTR entry in Reverse Lookup.