mail.builder.eserver.net has no MX records.
Question and response
Question
dig mail.builder.eserver.net. MX
Answer
The response has no answer records.
Authority
builder.eserver.net. 10800 SOA ns2.sk.eserver.net. info.eserver.ru. 2025092601 10800 3600 1209600 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0