Re:: to my previous post....
It turns out, after I have disabled iCloud on my MacMini ( I deslected all options, and signed out from iCloud ) and ater restoring the phone one more time to iOS5.0, now everything is working just fine.
I am pretty sure, I didn't have to restore the phone
(turn off the phone, then enter DFU mode by pressing power+home button for 10seconds untill black screen, then release power button and keep holding home button for another 10 seconds, doing all this with iTunes started)
and it would have been sufficient to just disable all iCloud settings on my Mac and sign out from iCloud but I can't be now 100% sure which one did it.
During the restore, I chose "Do not use iCloud" when asked.
I have deleted iCloud from phone prior to all these actions, but it did not help. It might be necessary though, to sign out from iCloud from your devices.
Now, Mail settings can be accessed, I have setup my Gmail and Yahoo accounts with no issues. Everything works just fine.
Now, I will have to search for iCloud documentation, because it definately needs better understanding.
iCloud takes presedence over all your settings and it is not clear in what manner it is doing it.
I hope this helps, and good luck.. 🙂