mail6253.m.fastwebmail.com has no NS records.
NS records for this zone are defined at fastwebmail.com.
NS records for this zone are defined at fastwebmail.com.
Question and response
Question
dig mail6253.m.fastwebmail.com. NS
Answer
The response has no answer records.
Authority
fastwebmail.com. 900 SOA ns-1883.awsdns-43.co.uk. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0