Free emailing

Hello guys, Im looking at setting up a mail server which will allow the public to register and access email from my domain, for example like Gmail, yahoomail, and hotmail. Is there software out there which can help me set this up, I have looked up and found squirell mail and round cube etc. the problem with these is that they are have to be linked to an IMAP server which is fine, but then with those I have to be the one to set up my users, can somebody help on how to that