Mailboxes missing on new iPad

I have connected to iCloud and set up all my email accounts on the iPad, but nearly all of my main email accounts mailboxes are missing. If I go into settings and select MAIL, the relevant Account and then select ADVANCED, under MAILBOX BEHAVIOURS is a list - Drafts/Sent/Deleted/Archived. If I select any one of them it brings up a page with all the mailboxes listed under 'ON THE SERVER'. I cannot open any folders just select with a tick which them changes the folder from Draft/Sent/Deleted etc.

If they are all listed there - why can't I get them on my MAIL app and where are all the thousands of emails in them ??

Access to all my emails while moving around was one of the key reasons I got the iPad. (9th Generation WiFi)