mail.sierracases.com has no NS records.
NS records for this zone are defined at sierracases.com.
NS records for this zone are defined at sierracases.com.
Question and response
Question
dig mail.sierracases.com. NS
Answer
The response has no answer records.
Authority
sierracases.com. 1800 SOA suzanne.ns.cloudflare.com. dns.cloudflare.com. 2398541592 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0