I have two Exchange 2010 servers I manage at different clients where I'm experiencing the same problem. The Exchange anti-spam is enabled on both servers in question. What's occurring is, email sent from specific domains is being rejected regardless of the fact that I have the IP Allow List enabled on each with the sending IP of the problem email domain listed. Despite the IP's appearing in IP Allow List, the server continues to block the messages. I have double verified that both the IP Allow List is enabled and that I have the correct IP addresses listed. I know it's Exchange blocking the messages after reviewing the transport logs where the reason for rejection states, "550 5.7.1 Sender ID (PRA) Domain Does Not Exist." I do have Sender ID enabled and verified that the email domain of this specific sender does not have a SPF record created so it makes perfect sense that the Sender ID test would fail and reject the message aside from the fact that I have it on the IP Allow List. I'm not sure if something is possibly taken precedence over the IP Allow List? I could disable the Sender ID but I'd prefer to know what's causing the issue.
Thanks in advance!