I was once getting unwanted emails from someone I knew. They were being sent from the person's workplace. Rather than just deleting them, I moved them to the Junk email folder. That trains the ISP's Junk filters to recognize emails from that origin as spam and weed them out. I subsequently heard it through the grapevine that the person was having problems getting business emails through to customers. I wonder how that could have happened? I didn't hear from them anymore.