> How can we as ESPs respond to them appropriately with removal of these people who don't want our emails anymore, if we don't know who the user is?

1. Don't send spam

2. ???

3. Profit!

Literally _all_ email that I've blocked has been from companies where I uncheck the box "send spam to me" and the company sends it anyway, or where the company thinks "oh this guy bought stuff from us, we can now send our daily/weekly/fuckly marketing spam!" or "we got your email from whatever shady place, and now we're sending you our information because you're in our industry" or stupid shit like that.

Gmail does not have a "block everything from this domain feature". I would love to block whole domains from my gmail account. Alas, I run my own email server to achieve it.