smtp-sofia.digsys.bg has no CNAME records.
Question and response
Question
dig smtp-sofia.digsys.bg. NS
Answer
The response has no answer records.
Authority
digsys.bg. 9306 SOA ns.digsys.bg. hostmaster.digsys.bg. 2026022502 28800 3600 2400000 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0