How do I block an email address on iPad?
How can one block emails from a sender on iPad email?
iPad (4th gen) Wi-Fi, iOS 11.0.2
Your best bet is to go your email account through safari and sign in, the blocking process is dependent on your email account i.e. gmail, hotmail, yahoo mail, naver mail ...etc.
Blocking emails through mail app is not available, because the process may be different depending the your email provider.
Hope this helped