mail.leaseweb.com has no CNAME records.
Question and response
Question
dig mail.leaseweb.com. NS
Answer
The response has no answer records.
Authority
leaseweb.com. 30 SOA ns0.leaseweb.com. postmaster.leaseweb.com. 2026022401 7200 1800 604800 30
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0