mail3.a1.bg has no CNAME records.
Question and response
Question
dig mail3.a1.bg. NS
Answer
The response has no answer records.
Authority
a1.bg. 300 SOA ns1.a1.bg. sysadmin.a1.bg. 2026030501 3600 900 1209600 43200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0