Update.-- After experimenting with my iCloud e-mail account I learned why the e-mails disappeared. When I updated my iPad recently, Apple automatically added my iCloud account to the iPad. Seeing all those receipts on my iPad, I erased them. That in turn erased them from iCloud which in turn erased them from my Mac iCloud account.
Lesson learned. Don't trust Apple to decide what you can and can't do on your iDevice. I didn't mind my iCloud being there, just not all the e-mails visible to anyone looking at my iPad. I just wanted the new ones which I can keep or erase. I can't do that according to Apple.
Original post.-- I went to check my iCloud e-mail today and discovered it was all gone, e-mails going back years documenting all my purchases with Apple in their stores and on-line (App Store and iTunes). Gone, like a very empty mailbox.
Fortunately I keep a copy on my Mac, but it only goes to show me the iCloud really isn't that reliable and goes to show anyone, if you trust them, you better hope they don't screw it up and lose it, like they have my e-mail.
It's their new slogan, "The Cloud, everything you trusted with us, Gone with the Wind."