- Proactive prevention of an issue; things like listing of dynamic and non-SMTP space; things that shouldn't connect to your mail server, and if they do, that alone is typically a spam sign.
- Reaction to a specific issue, like spam received from a server. From where one spam message comes, more are likely to follow.
- Spam support, somebody in league with spammers or providing some sort of service to spammers.
- Protect my network. I'm receiving spam from this IP address, so it's fair for me to protect my users by not letting any more spam through from this IP address.
- Push the bad guys to reform with a combination of carrot and stick. While you're bad, you can't mail me. When you change to be good, I'll let you email me again.
- ???????? NYARRR, I'M ANGRY!! The sort of mentality where they say, to hell with you, you don't deserve to be able to send email to anybody ever again. Sometimes validly so, but do the people this gets aimed at really end up going away? And, is it always merited? The beatings will continue forever, no matter what, there's nothing you can do about it.
It's easy to say "nobody should send spam ever," but there's a long history of blacklists helping to improve the email ecosystem by engendering change; by pushing bad senders to become good senders. Right?
I'd be curious to hear any thoughts y'all might have on this topic. What's the best possible policy for a blacklist in this situation? Why does it matter, or why doesn't it matter? Your feedback welcome.