From the early days of the public internet:
The reflector bomb works on the simple principle that mail sent with spoofed addresses will bounce to the victim. Its particular agent is the BCC line, which enables the mailbomber to list any number of fake addresses on diverse servers for greater inefficiency of routing, leading to a wider variety of incoming paths to the target. – “Reflector Bombing; Mail Mayhem,” Textfiles.com
Back before the internet got civilized, it was still possible to mailbomb with impunity. Now, with log-files and verified mail and very few open servers (thanks to the spam epidemic), it’s almost impossible. But back then, it was delicious. Read on for an account of how insane vandalistic mail-bombers paved over sites with garbage bytes and blasted servers into the aether.