To resolve the issue, allow connection from internal servers:
- Make sure that the IP of the MailServer is added in the approved list for IP Filtering. From the console, go to IP Filtering > Approved List to check this.
- Back up /opt/trend/imss/postfix/etc/postfix/main.cf.
- Open /opt/trend/imss/postfix/etc/postfix/main.cf and look for the "smtpd_client_restrictions" key.
- Add the "permit_mynetworks" on the "smtpd_client_restrictions" key similar to:
smtpd_client_restrictions = permit_mynetworks,
hash:/opt/trend/imss/postfix/etc/postfix/NRSAllowAccessList {...Other original values}
(permit_mynetworks has to be the first value in the list) - Restart Postfix. Check this Postfix readme file for more details about Postfix. Follow the instruction for mynetworks_style (default: subnet).