The Symantec Messaging Gateway 10.5 appliance will be deployed with the following topology: Internet Default Gateway (10.10.10.1) <--> Email Gateway (10.10.10.11) <--> Symantec Messaging
Gateway (10.10.10.21) <--> Internal Mail Server (10.10.10.31)

Which IP address should be specified in the Mail Filtering - Non-local Mail Delivery page of the site setup wizard?