I'm going to shortchange you here as I would guess you would have already google'd "What are the msn.com IMAP settings?" already.
We know that Outlook.com and the mail app on Windows 8 does not support pop3 so it's a safe bet it does imap.
But I'm a little confused. Why must it be IMAP? I have yet to find any email app so far not do both common systems.
Until Windows 8 that is.
I know an elderly couple that have used an email address that ends in "msn.com" for years. Their old Windows computer is failing so they are purchasing a new iMac. Is there a way to get their msn.com email account to work with the Mail app? I don't think that account supports IMAP and its difficult to reach msn.com support. Would appreciate any assistance.