I have one customer that we cannot send emails to. I get the 451 4.1.8 Possibly forged hostname for **.**.***.130 error. Here is the problem, I have no idea why it is getting the ip address it is getting. I have internal DNS set correctly. I have external DNS setup, all of my ptr, a records, spf, etc. are all setup and correct. For some reason though this email is getting the IP address of my VPN. My email is **.**.***.134 and my VPN is **.**.***.130. There is nothing that points my VPN to my email.
But when a user tries to send to this one email address it returns this error. Like I said I have checked internal DNS, I have checked my external DNS, I have checked my firewall, etc. I am not sure where else to look. I am not even sure this is on my end.