When you use the Proxy activation, the machine from Domain 2 in VAMT will first attempt to activate against the KMS server in Domain 1 instead of going to the Internet.
However, if your Alternate site is left blank while setting up the VAMT, it will cause the machine to check MS (over the Internet) if it can't find your Server right away and also can cause Dual Scan issues.
And also for your information you can use the Volume Activation Management Tool (VAMT) to perform activation for client computers that do not have Internet access. The client products can be installed with any type of product key that is eligible for proxy activation: Multiple Activation Key (MAK), KMS Host key (CSVLK), or retail key.
Hope this resolves your Query!!
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