_mailsrv6.tolna.net has no CNAME records.
Question and response
Question
dig _mailsrv6.tolna.net. NS
Answer
The response has no answer records.
Authority
tolna.net. 7841 SOA ns3.tolna.net. support.tolna.net. 2020052878 86400 7200 3600000 172800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0