mail.twoople.com has no NS records.
NS records for this zone are defined at twoople.com.
NS records for this zone are defined at twoople.com.
Question and response
Question
dig mail.twoople.com. NS
Answer
The response has no answer records.
Authority
twoople.com. 600 SOA a.share-dns.com. master.share-dns.com. 1765260472 3600 1200 86400 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0