mail.srvnl.nl has no CNAME records.
Question and response
Question
dig mail.srvnl.nl. NS
Answer
The response has no answer records.
Authority
srvnl.nl. 6042 SOA ns1.naamservert.nl. hostmaster.naamservert.nl. 2026030501 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0