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 target

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 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.