But that's what spammers do!

A few weeks ago I was asked my opinion about a delivery situation. It seems that a sender wanted to mail to a purchased email list. They asked what I thought about getting fresh IP addresses and domains to use to send mail to the purchased list. “We know we’re going to get complaints, probably hit spamtraps and generally have problems with the first few sends of the list. We want to do this without harming our reputation. We figure if we move over to different domains and different IP addresses than we can send this mail and not suffer a reputation hit.”
Uh. Yeah. That’s what spammers do. They split off their mail into discrete sets so that they can spam with impunity and still have one or two ranges that have a good reputation and decent delivery. Some spammers have taken the discrete companies to extremes, and have a series of companies. They purchase a new list and send it through their companies one by one. At each step, they aggressively purge off bounces and complainers. Gradually, they move the list through their steps, resulting in a list that generates few complaints that they can send through their high reputation companies with few delivery problems.
Sure, legitimate mailers can do the same type of thing. But how legitimate can a sender be if they are using spammer tactics? And these are not mailers unwittingly doing something that spammers also do, these are mailers who are using spammer tactics for exactly the same reason spammers do it. They are trying to send mail people do not want, but send it in a way that does not negatively affect their bottom line.
Spammers hide and try to avoid their bad reputation. Legitimate mailers do not.