I'm getting the following error when sending to only a couple of recipients
"You do not have permission to send to this recipient. For assistance, contact your system administrator.
<xyz.123.com#5.7.1 smtp;550 5.7.1 Access denied. Cannot resolve PTR record for x.x.x.x>"
The server name and IPs have been changed for security reasons.
can someone guide me on where to start in troublshooting this issue. We are waiting for a real email admin to start soon and I'm just covering till then. Thank you.