Why am I here?

You probably found the URL for this page in a SMTP rejection notice that looked similar to this:

<name@example.domain>: host ra.horus-it.com[65.108.3.114] said:
554 5.7.1 Policy violation; see https://www.horus-it.com/policy3/?X=Y

What does it mean?

The owner of address name@example.domain has decided to only accept correspondence from a list of known contacts, which is usually done to counter address harvesting, and your sender address was rejected because it is not a member of said list.

How can I register as a contact?

If you have a legitimate reason to send email to this particular recipient address, please write to postmaster@example.domain first. State the full sender and recipient addresses, and explain why you require clearance. If the recipient agrees to accept your request, you will usually receive a notification within two working days.