We then got the recommendation of a company (cannot remember their name) that could analyse our IPs and give recommendations. Naturally, the recommendations were the ones that you could find everywhere so they were not useful, but the company did have access to MSFT's score of our IPs, so we could know when we were close to being blacklisted and could take action/ramp down/etc. How did they have access to those internal IP scores? I don't know, but it seems totally fishy :).
For sure we spent 5k+ USD yearly in this service (which is a huge amount of money in a 3rd. world country), and "somehow" after paying our deliverability did improve, despite doing the same things as before, as the recommendations were not ingenious.
So yeah, e-mail deliverability is a mafia, for sure.
I felt outraged at the moment because it was clearly a "pay-to-play" scheme, but ~8 years ago the number of Hotmail/Outlook addresses in my country was definitely substantial. Probably it still is.
How did they have access to those internal IP scores?
When I was doing DMARC stuff professionally, plenty of big names were willing to send DMARC reports our way. Microsoft was the only company to give us full text.But the score I am speaking of was something different: it was the reputation assigned by Microsoft (i.e., something internal) to the IPs from which we sent e-mails. This score was used to determine how many e-mails sent from those IPs would pass/fail MSFT's filters. And to have access to the score and improve it, we had to pay a 3rd. party :).
Thanks for mentioning this. Have set DMARC preferences in DNS for ages but never configured a mailbox to receive the reports. Will try it out.
That's not necessarily unreasonable, depending on which provider that is.
Sites like Wikipedia also block entire ranges to prevent spam. Unfortunately sometimes people do get caught up in that (as I did last year).
All mail providers mass block IPs, because the spam from some ISPs is literally too much to even filter.
I run a few high volume (very legitimate) servers and it's been a huge pain in the butt to keep them off of blacklists, but at the same time we've also had spammer problems and I totally get it.