mx.ascentymail.com has no NS records.
NS records for this zone are defined at ascentymail.com.
NS records for this zone are defined at ascentymail.com.
Question and response
Question
dig mx.ascentymail.com. NS
Answer
The response has no answer records.
Authority
ascentymail.com. 1200 SOA a.dns.ascenty.com. registro.ascenty.com. 2019070205 28800 7200 604800 86400
Additional
. 0 OPT ; payload 2800, xrcode 0, version 0, flags 0