What's not to like about mxtoolbox.com?

Question

Mail server

We have a domain its-krd.xyz
mxtoolbox.com writes an error Reverse DNS is not a valid Hostname
how many googles this error concerns exactly the fact that the mailer is not on a subdomain, I transferred the mailer to a subdomain: mail.its-krd.xyz and ptr did on mail .its-krd.xyz.
ptr 193.8.46.95.its-krd.xyz. 3600 PTR (reverse entry) mail.its-krd.xyz.
still the same error. And something became unclear with ptr (193.8.46.95.its-krd.xyz. ). Now it is possible to swear on the PTR. But when the mailer and ptr are correct on the domain, the error is the same.
What could be the problem?
the error itself

Answer 1

attributed as follows:
93.8.46.95.mail.its-krd.xyz.
3600
PTR (reverse entry)
mail.its-krd.xyz.
based on the recommendation "if the addresses of the domain and the mail server do not match, then the PTR record should be created specifically for the MX record."