ruweb.deserv.net has no MX records.
Question and response
Question
dig ruweb.deserv.net. MX
Answer
The response has no answer records.
Authority
deserv.net. 3600 SOA dedns.deserv.net. root.deserv.net. 2021042601 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0