Cannot see old emails in my iCloud account

The problem is I cannot see any of my past emails other than the ones that have come in since I received an email from Apple stating my iCloud storage was full. When I contacted Apple they stated that there was lots of room on my account. Over 15 Gb on my 20 GB account. I tried backing up, using iCloud backup, my iPhone 4s and iPad, I have an old iMac which can only run Snow Leopard. I wonder if this might be the problem? Anyone else experiencing the same issue?