I just received my new 27" iMac last week and transferred my files and settings using the migration app in the Utilities folder from my 17" MacBook Pro. My system works great with the exception of not being able to connect Apple Mail and Notes to my iCloud account. In my case, it resolves to the p02-imap.mail.me.com server.
Apple support tried hard to get this working for me - I was asked to delete my current email account then try to recreate it from System Preferences/iCloud. I was told that the system was unable to communicate with the p02 server at this time - to try it from Apple Mail instead. Notes - I was told to try again later. The Apple support tech had me create a new test account and go back to the iCloud preferences. That also failed. We tried changing DNS settings and several other things that also failed.
Finally, he asked me to reinstall Mountain Lion. I did that as well - but it did nothing to resolve the problem.
Yesterday, he called back to ask if I could carry the system to a nearby Apple Store to see if I could connect via their router. No? Then maybe I could start fresh and MANUALLY go back to factory and reinstall MANUALLY all my programs and re-establish all my settings to resolve the problem.
These are great ideas for an act of desperation, but, as I reminded him, my Outlook account connects to the same server just fine. So... I'm baffled as to the problem's resolution or cause at this time.
I do appreciate the effort Apple techs put into these things though.
Ron