This kind of outage really scares me away from using iCloud as my primary mail service.
I use a few domains hosted through google/gmail and its rock solid, can be accessed on any type of device.
I don't understand how someone relies on @mac/@me/@icloud for serious mail use.
First time any problem from .mac/.me/cloud has affected me in any noticeable way. Using the internet as a primary resource for communication and assuming it is infallible is the problem. Outages happen.