mx100.atlex.ru has no CNAME records.
Question and response
Question
dig mx100.atlex.ru. NS
Answer
The response has no answer records.
Authority
atlex.ru. 10800 SOA alpha.atlex.ru. noc.atlex.ru. 2026020400 28800 7200 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0