DOMAIN_NOT_RESOLVED

DOMAIN_NOT_RESOLVED

Receive error from mail.zoho.com :
"
----- The following addresses had fatal errors -----

[Status: DOMAIN_NOT_RESOLVED, Address: <'xxx@XXX.gov.ua'>, DOMAIN_NOT_RESOLVED]

Message will be retried for 4 more day(s)

"

But MX, ports on server xxx.gov.ua - open, and received mail from another services(Outlook.com)

Any reason wny?