I am using the 25 GB plan for iCloud. This morning I got the message in Mail.app that my iCloud storage is full. However, the iCloud system preferences tell me, I have still 11 GB left. In MobileMe I could set the split on how much would be used for my Email account. How can I increase the Email storage with iCloud?
iCloud mail space should be dynamically increased as you go. There is nothing users can do to manually expand that size. If it is stuck for you, I recommend contacting Apple at their support web page for iCloud, as you are a paying customer, you sure are entitled to great service.