mail.long-edu.ru has no MX records.
Question and response
Question
dig mail.long-edu.ru. MX
Answer
The response has no answer records.
Authority
long-edu.ru. 3600 SOA vip154.hosting.reg.ru. support.reg.ru. 2022091351 10800 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0