mail.doubleservice.com has no NS records.
NS records for this zone are defined at doubleservice.com.
NS records for this zone are defined at doubleservice.com.
Question and response
Question
dig mail.doubleservice.com. NS
Answer
The response has no answer records.
Authority
doubleservice.com. 900 SOA ns-1840.awsdns-38.co.uk. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0