I just got an email from Mailboxpark who seem to be doing this. It looks like they set up catchall mailboxes for the domains, then filter the spam sent to that mailbox and sell details of it to spam prevention companies and pay the domain owners a bit for use of the domains
I know some users who use specific landing pages on their domains. And they collect user emails. And once inside the list they give our weekly newsletter. And this way more traffic is diverted to the advertising pages. This method has worked for many people. I have seen this working too. But it all comes down to how some people prefer to make money off the mailing list. Not a lot of people can get it properly.
I set up small sites to promote my actual sites that I was working on. Articles and redirects and backlinks can really help search rankings. Letting people sign up for my emails through it worked really well.