Symantec Messaging Gateway (SMG) is experiencing delivery issues, and is using a public DNS server.
Examples might be 184.108.40.206 (provided by Google), 220.127.116.11 (provided by Level 3), 18.104.22.168 or .220 (provided by Cisco/OpenDNS).
Free public DNS hosts are not recommended. Issues with these hosts include:
The recommended order of DNS host configuration is:
For further reading, please review the Administration Guide for Messaging Gateway.
For more information about public DNS service and SLAs, please see each service's respective websites.