[caeruleus]

Afaik, it is specific to this provider. I'm not entirely sure why exactly tbh, probably to require some kind of associated identity (the policy is likely targeted to larger providers). It was a manual process and I never had to do anything similar for a different one.

They require that

a) the sending IP address has a PTR record b) from a domain that you own c) that resolves to the same IP address.

This is also very important for general deliverability (https://en.wikipedia.org/wiki/Forward-confirmed_reverse_DNS).

They furthermore recommend d) that your host name should clearly mark it as a mail server and e) to make sure the domain leads to a web page that contains provider details and contact information.

[ssl232]

When I hosted my own mail I did all of that except (e). I had trouble, as seems to be typical, with deliverability to Microsoft-hosted addresses. I wonder if (e) would have helped (doubt it).