Microsoft allows users to sign up for Hotmail and then add additional hotmail email addresses using their country domain. For example, if you are a US resident, you can sign up for a hotmail.com email address ,then add an alias @hotmail.us address but you have to use your @hotmail.com to sign-in into your Windows Live Hotmail account and other services. The advantage of using a country-specific alias email domain is that you can use it when your preferred @hotmail.com name has been taken.
Alias country specific email domains cannot be used to log into your Hotmail account or services.
Windows Live ID
Alias Email Addresses
USA MSN Home Page
Windows Live Sign In – USA English