frontend.hexonet.net has no MX records.
Question and response
Question
dig frontend.hexonet.net. MX
Answer
The response has no answer records.
Authority
frontend.hexonet.net. 3600 SOA ns1.hexonet.net. hostmaster.frontend.hexonet.net. 2024051392 86400 7200 3600000 172800
Additional
. 0 OPT ; payload 1400, xrcode 0, version 0, flags 0