imap.host.ctl.one has no NS records.
NS records for this zone are defined at host.ctl.one.
NS records for this zone are defined at host.ctl.one.
Question and response
Question
dig imap.host.ctl.one. NS
Answer
The response has no answer records.
Authority
host.ctl.one. 300 SOA ns3.level3.net. postmaster.ns3.level3.net. 2026012700 300 240 86400 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0