Hosts file would be your first way assuming you trust MS to honor that convention. You can always consider using a way that is not reliant on Windows goodwill ( for example, Pihole would allow you to limit various unwanted IPs based on your custom list; technically, your router should be able to do it too, but it varies wildly by mfctr/model ). That said, I am not that familiar with that functionality in Excel and it is not a given that it would fail gracefully if it is actually stopped from calling mothership.