This issue occurs if the outbound IP address for the domain is not added. Only the IP addresses configured as outbound servers for a particular configured domain are allowed to send emails through the Trend Micro Email Security relay email servers.
Follow these steps to resolve the issue:
- Log on to the Trend Micro Email Security web console then go to Domains page.
- Click the related domain which will send the outbound mails to Trend Micro Email Security.
- Make sure that Enable outbound protection is checked.
- Specify all the IP addresses of your outbound servers in the Outbound Servers configuration for that domain so that Trend Micro Email Security can accept emails messages from these servers.