ns.pulkov.spb.ru has no MX records.
Question and response
Question
dig ns.pulkov.spb.ru. MX
Answer
The response has no answer records.
Authority
pulkov.spb.ru. 3600 SOA ns.nalitch.spb.ru. rconst1.yandex.ru. 2020082500 10800 3600 432000 38400
Additional
. 0 OPT ; payload 1680, xrcode 0, version 0, flags 0