You want to know what the difference is between "Use internal DNS server" and "Use the following external DNS servers" in the DNS tab of the Host Configuration of your appliances.
The option "Use internal DNS server" will configure the appliance to use its internal DNS caching server to directly query the internet DNS root servers for non-cached name resolution (forwarder)
The option "Query source port" will force the DNS query to use the configured port as its source port when connecting to the internet DNS root servsers.
The option "Use the following external DNS servers" will configure the appliance to use its internal DNS caching server to directly connect to the DNS servers at the configured IP address(es) for non-cached name resolution (forwarder). These servers can be DNS servers that are either internal or external to the local network.
Technical Information The Symantec Brightmail Gateway appliance uses an internal caching DNS server that will forward uncached name resolution queries to the configured servers.
Imported Document ID: TECH94299
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