1) Wifi Filter
Being one of the many people in the world to have iPads, paid by my district, at school, this too has happened to me when I set up my mail account in the 'Mail' app. Most likely, the wifi is the problem, with the wifi having a filter. For example, when I tried going to gmail.com at my school's wifi, I was denied because they have a filter that blocks websites. So, as goes for restricting websites, the app follows through with not going to that website.
2) Account Settings
Simple. Maybe you put your email and password incorrectly? Check. (Setting>Mail, Accounts, Calenders. Under accounts, click the tab for your email, make sure the address is correct, if not, click the address, type it correctly, and also, to be sure, type your password again)