My MobileMe account is not receiving any mail from hawaii.rr.com servers anymore. This is a problem for me because they are the main ISP out here (TimeWarner / Roadrunner) in Hawaii. Also it's my boss's email provider - at least the problem was reproducible.
So... The hawaii.rr.com accounts do not get a message undelivered warning. I am able to send to the hawaii.rr.com accounts from the MobileMe account. The hawaii.rr.com accounts are sending and receiving all other mail correctly. Nothing is ending up in junk mail filters. I have not transitioned to the iCloud. I have tried both the .me and .mac variations on my email.