frontend.ptn.ru has no MX records.
Question and response
Question
dig frontend.ptn.ru. MX
Answer
The response has no answer records.
Authority
ptn.ru. 3600 SOA ns1.ptn.ru. root.ip.rostelecom.ru. 2025031802 86400 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0