mail.emailsrvr.com has no NS records.
NS records for this zone are defined at emailsrvr.com.
NS records for this zone are defined at emailsrvr.com.
Question and response
Question
dig mail.emailsrvr.com. NS
Answer
The response has no answer records.
Authority
emailsrvr.com. 300 SOA ns.rackspace.com. postmaster.emailsrvr.com. 1756450505 3600 300 1814400 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0