At the Windows Live Custom Domains
site, you can sign up to receive unlimited domain name email addresses for a domain name that you already own or you can purchase a domain through one of the site's partners. The free service is hosted and managed by Microsoft, so you don't have to worry with equipment or scale issues and can just focus on running your business.
The Custom Domains
service also lets you manage your domain accounts online using the provided web tools or you can allow your site's visitors to create their own accounts using open membership. These custom domain name email addresses work out-of-the-box with Windows Live and MSN services, like Messenger and Spaces and have 2 GB of storage per mailbox. The service is initially limited to 100 email addresses at first but can be upgraded for free to an unlimited number by completing a short questionnaire.