MS Exchange 2013 Error 550 5.7.1 bounceback

After spending a while trying to figure this out and without going into the many steps I tried after all of the clients users could send mail but could not receive any mail from external sources (internal mail was fine). The external mail was all bounced back with the following:

• Delivery to the following recipient failed permanently: user@domain.com
• Technical details of permanent failure:
• Google tried to deliver your message, but it was rejected by the server for the recipient domain domain.com by webmail.domain.com. [0.0.0.0].
•  The error that the other server returned was:
• 550 5.7.1 Unable to relay for user@domain.com

On possible fix and the quickest to try (hopefully you will avoid all of the longer tests I have carried out today).

In the The Exchange Admin Center (EAC) click on “Mail Flow” (on the left menu) then on “Receive Connectors” then select “Frontend RECV Connector” and click the edit icon. Select “Scoping” and edit the “Network adapter bindings” change “All IPV4 Available” to the IP address of your Exchange Server.

This worked after many hours of reading and head scratching on a single IP address server, I hope it helps.