ns1.zsttk.net has no MX records.
Question and response
Question
dig ns1.zsttk.net. MX
Answer
The response has no answer records.
Authority
zsttk.net. 86400 SOA ns.zsttk.ru. hostmaster.zsttk.ru. 2021052709 43200 3600 2419200 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0