266938 Real email wanted

I need this software that would allow every register user to have there own email address userID(at)mywebsite.com. It has to be like regular email fully functional, has to be able to send and receive emails from other email websites like hotmail or yahoo, etc. I could probably say it would be a clone of hotmail, with a few changes. (Don't know what programming options needed for this job, picked everything I knew, doesn't have to be)