MTA-STS policy host
ydfnzp70bb2qsdw5.mta-sts.ruareports.com
This name is the CNAME target of one RUA Reports account. It serves the MTA-STS policy files of that account's domains, and nothing else. The certificate you see was issued for it on purpose: your setup works.
To publish a policy for a domain:
- Enable hosting on the domain's MTA-STS tab and save a policy.
- Add a CNAME from mta-sts.<your domain> to this name.
- Publish the _mta-sts TXT record with the policy id shown on the tab.
Sending servers then read https://mta-sts.<your domain>/.well-known/mta-sts.txt.