Component: Symantec Messaging Gateway
This is usually the result of a firewall or other network device which is preventing the SMG system from connecting to the internet on port 443. Please see the product documentation for a list of required TCP ports for Messaging Gateway
This issue is usually caused by an intermediate network device or firewall intercepting the TLS negotiation with https://register.brightmail.com and attempting to perform a TLS inspection on the connection. TLS inspection is not currently supported for Messaging Gateway connections to the registration or rule update servers. The SMG IPs will need to be white-listed in whatever network device is intercepting the TLS negotiation.
If you are on SMG 10.6.5 or older see this below document:
https://knowledge.broadcom.com/external/article/189124/messaging-gateway-1065-and-earlier-canno.html