How to solve the problem when sending mail (MX records)?

Question

Mail server

Good afternoon friends. When sending a letter from this mail to some addresses, it gives the following error:

[email protected]>: host mail.slon26.ru[77.39.4.27] said: 550-Verification failed
for <[email protected]> 550-It appears that the DNS operator for
volvonev.ru 550-has installed an invalid MX record with an IP address
550-instead of a domain name on the right hand side. 550 Sender verify
failed (in reply to RCPT TO command)

As I understand it, the MX record is incorrect, but I myself don’t understand what. Mail is processed by their server, ours is redirected:

Answer 1

Wrong entry in DNS
The server should have a name, not an IP address.
That is, in the DNS write A-record: blabla.volvonev.ru 31.13.248.114
and MX-record: blabla.volvonev.ru.
And don't forget to fix the PTR