mail.mailtrap.live has no CNAME records.
Question and response
Question
dig mail.mailtrap.live. NS
Answer
The response has no answer records.
Authority
mailtrap.live. 1041 SOA graham.ns.cloudflare.com. dns.cloudflare.com. 2396631759 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0