I was having problems mailing to Outlook customers with my personal domain (some of these email providers are HUGE pains when it comes to detecting "spam") and finally got a tech to send me this handy list of feedback loops for various bit email providers. If you send your own newsletter and worry your IP might be blocked (or it has been) be sure to sign up for at least Yahoo, Outlook and Gmail loops. When you do, they send complaint notices to you so you can remove those people --- which is a pain but a lot better than getting your whole system blocked because people repeatedly complained and you didn't know about it! Sadly, some people would rather report senders as spam than just unsubscribe. 😂
