Hi there,
About 3 weeks ago, my Exchange 2010 server starts to have issue sending email to particular domains (more than one domains). The sender get a bounce back message said that "Delivery is delayed to these recipients or groups".
The Exchange 2010 server's last error in Queue Viewer is 421 4.4.0 Remote server response was not RFC conformant.
The workaround that I did was creating the second Send Connector to ForceHelo for those trouble domains. The problem is, the number of trouble domain keep increasing. I could not keep adding these domains to the second Send Connector.
I am using Dyn Email Gateway service, which the MX is pointing to mx1.mailhop.org and mx2.mailhop.org. Is this something to do with PTR and SPF records? The domain name is ncca.org.au.
Could anyone help me to solve this issue?
Thank you for your help in advance.