On July 31st 2012, Microsoft launched Outlook.com a FREE, Unlimited E-mail service similar to Gmail. This service will also support upto 500 FREE signups with the same set of features with a custom domain name.
This is similar to Gmail with Google Apps except you get 490 more signups and NO storage limits on mailboxes!
Your users can also import all their e-mail from Gmail or any other POP-supporting e-mail service, and sign-in to check ALL their e-mail at YOUR website!
Check out the link below to do it yourself in 5 easy steps: