Error 421 4.4.0 [internal] failed to connect: no mail servers for this domain could be reached at this time.
Attempted Delivery to: default-non-local-route
Last error: Error 421 4.4.0 [internal] failed to connect: no mail server for this domain could be reached at this time.
If outbound delivery to most domains is working as expected and the issue is limited to a small number of domains / mail routes, the issue is likely with the destination mail server
If all outbound email is failing with this delivery status, the issue is likely the SMG configuration
Set the Non-local messages in the Advanced SMTP configuration to use the Outbound_IP. Check the information and set the Advanced SMTP configuration to the requirements of your organization.
telnet -b inbound_ip remote_server_ip 25
Connection refused (Unsuccessful)
telnet -b outbound_ip remote_server_ip 25
Connected to remote_server_ip (Successful)
For complete details on how to test mail delivery issues, reference the section, "Outbound messages in the delivery queue are not being delivered" in the document, Troubleshoot email delivery issues using telnet