Determining country by source ip is pretty accurate.
Sure, but not having the ability to access smtp.live.com and pop3.live.com
would imply firewall rules that prevent US IPs from accessing them.
Clearly, though, those two servers have IP addresses in Microsoft's network
(65.55.172.254 and 65.55.172.253) and I can't think of anything that non-US
clients would do that is different from what US clients would do, so it's
not like there would be a functionality change.