tarpitting

Adding a delay between e-mail messages in order to thwart spammers. A mail server can be set up to insert delays between messages when a single e-mail has a large number of recipients. It could start delaying after the first 25 messages were sent, which would have little effect on legitimate users, but would considerably slow down the spammer. For example, if a five-second delay were added to a million messages, it would take 60 days to release them from the mail server. The term comes from "tar pit." If you fell into one, you would be slowed down.