I am experiecning the same issue.
I have verified that:
I am unable to receive any emails from any RoadRunner emails to my iCloud email address.
I am able to send messages from my iCloud email address and receive them to both my iCloud and RoadRunner accounts.
I am able to send messages from my RoadRunner account to my RoadRunner account.
I am able to send messages from my RoadRunner account, but am not able to receive them on my iCloud account.
This seems to have started on or around January 25, 2013. Up until then, I have been able to communicate all ways stated above with no issue.