mxfront.stable.qloud-b.yandex.net has no SRV records.
Question and response
Question
dig mxfront.stable.qloud-b.yandex.net. SRV
Answer
The response has no answer records.
Authority
stable.qloud-b.yandex.net. 300 SOA ns3.yandex.ru. sysadmin.yandex.ru. 1772552115 900 600 3600000 300
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0