mail.mutare.com has no NS records.
NS records for this zone are defined at mutare.com.
NS records for this zone are defined at mutare.com.
Question and response
Question
dig mail.mutare.com. NS
Answer
The response has no answer records.
Authority
mutare.com. 180 SOA ns20.digicertdns.com. dns.digicertdns.com. 2009011665 43200 3600 1209600 180
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0