How to block emails from unwanted people?

Go to Mail page>>click options (top right)>>then click "block addresses". Enter their address and click "add block".

If you're using Beta or New Mail ??
Mail page>>options>>mail options>>spam>>block addresses.

Mail from that person will thereafter be deleted immediately upon arrival,you will never see it.
And,that person will receive no notification, at all, that their mail has been blocked.