You can't import a list of domains. However, you might find it easier to add domains directly to the registry.
As always, take precautions before editing the registry directly. Make sure you have a good, current backup of your system. Creating a fresh emergency repair disk and saving the registry key you?ll change before modifying it are good ideas as well.
Open the registry editor (regedt32.exe) and navigate to the following key: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeIMC\Parameters\. In the right pane, double-click on the TurfTable value. You enter the domains you wish to filter as a string, just as you would in the Exchange Administrator program. You can enter as many domains as you like, or paste the domain names from a text file, without all the mouse clicks needed in the Administrator program. If you?re entering more than a half-dozen domains at a time, this will save you time.
Restart the Internet Mail Service to make your registry edit take effect.