how do I block harassing senders, mail I don't want to receive

I am receiving harassing emails with unwanted suggestions (sometimes suggestions appear sexual). I want to block these emails from coming thru. I think they're from the same person, he/she just keeps changing their name & email addr, but most are from hotml. How can I block these emails? They are very offensive. I've already emailed hotml, talked with my provider and talked with the police. No help