When attempting to register a Symantec Messaging Gateway (SMG) appliance or virtual machine, the registration attempt fails with the message that the proxy server credentials are invalid even though the proxy server does not require credentials and no credentials are configured.
The configured proxy server credentials are invalid. Please check the proxy credential settings.
If the proxy server is attempting to do TLS packet inspection, the communcation with the Symantec operations center to register the appliance and license will fail.
TLS packet inspection operates as an authorized man in the middle in which the proxy server or router attempts to provide it's own certificate to the connection rather than passing the TLS connection attempt through to the destination server. Messaging Gateway will identify this and the secure connection will fail since the certificate that is being provided is not the Symantec operations center certificate.
Ensure that all (SMG) IP addresses are exempted from TLS packet inspection.
TLS packet inspection can interfere with not only product registration but ruleset downloads and software updates.