Component: Symantec Messaging Gateway
This issue is usually caused by communication blocks between where the product is installed and our authentication servers. Here is the best way to troubleshoot network connection issues:
command: nslookup register.brightmail.com
command: telnet register.brightmail.com 443
Connected to register.brightmail.com.
If you can't access your firewall or other appliance directly, get your network admin to watch the logs while you attempt to connect.
Have your firewall team or F5 team bring up real time logs and then try to connect/register the Gateway. Make sure the WAN port is set to 1500. Then test again.
If you are on SMG 10.6.5 or older see this below document: