mail.solver.net.ua has no CNAME records.
Question and response
Question
dig mail.solver.net.ua. NS
Answer
The response has no answer records.
Authority
solver.net.ua. 3600 SOA ns.solver.net.ua. root.margadon.kot.poltava.ua. 2026010601 86400 3600 3600000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0