mail.vortexservers.com has no NS records.
NS records for this zone are defined at vortexservers.com.
NS records for this zone are defined at vortexservers.com.
Question and response
Question
dig mail.vortexservers.com. NS
Answer
The response has no answer records.
Authority
vortexservers.com. 1800 SOA april.ns.cloudflare.com. dns.cloudflare.com. 2396318317 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0