ClickZ: The Unsubscribe Dilemma

Permission-based email lists continue to decline in effectiveness, at least partly because people are not unsubscribing to lists anymore. Sometimes they fail to unsubscribe because it's too much of a hassle. Other times, they've simply become habituated to ignoring the unsubscribe links they see at the bottom of most spam messages. Instead of reading the email lists, they just have their email programs filter them, causing declines in advertising effectiveness.