nussmtp01.ironmountain.com has no NS records.
NS records for this zone are defined at ironmountain.com.
NS records for this zone are defined at ironmountain.com.
Question and response
Question
dig nussmtp01.ironmountain.com. NS
Answer
The response has no answer records.
Authority
ironmountain.com. 900 SOA nusdnsgm01.ironmountain.com. please_set_email.absolutely.nowhere. 2005447553 10800 1080 1728000 900
Additional
. 0 OPT ; payload 1220, xrcode 0, version 0, flags 0