mx.directi.com has no NS records.
NS records for this zone are defined at directi.com.
NS records for this zone are defined at directi.com.
Question and response
Question
dig mx.directi.com. NS
Answer
The response has no answer records.
Authority
directi.com. 180 SOA usc4.akam.net. syseng-senior.directi.com. 2018110849 43200 3600 1209600 180
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0