Does anyone have any thoughts on this? Sorry if this is the wrong place to ask.
First of all, this strikes me as a legal and policy decision. For the legal aspects you should ask your lawyer or take it up on a legal blog like http://www.groklaw.net For the policy aspects, you really should take it to the RIRs where you have IP allocations. All RIRs operate policy discussion mailing lists. One disturbing thing that I saw in your message is that you seem to be accepting the fact that a so-called anti-spam organization can dictate how you operate your network and what requirements you must meet. I would suggest that this is the wrong way to approach the problem, rather like letting the tail wag the dog. It would be better for you to join an organization like MAAWG http://www.maawg.org/home which is attempting to define best current practices for ISPs. I don't know whether or not they have dealt with this particular issue yet, but it sounds like something that falls under their umbrella. -Michael Dillon