mail1.hostedrt.com has no NS records.
NS records for this zone are defined at hostedrt.com.
NS records for this zone are defined at hostedrt.com.
Question and response
Question
dig mail1.hostedrt.com. NS
Answer
The response has no answer records.
Authority
hostedrt.com. 900 SOA ns-1053.awsdns-03.org. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0