Email hacked

go to:

https://appleid.apple.com/#!&page=signin

Then reset your password from there. This should take of the problem.

Another possible cause is if you receive an extensive amount of emails and don't empty the email trash folder you might have run out of space. You would have to have an obscene amount of emails but if this is the case, empty the trash folder and clear out old emails. This will free up some space and you should start receiving them again.

If you had to guess, how many emails do you have?

Who is your email provider?