mailus1.syncreon.com has no NS records.
NS records for this zone are defined at syncreon.com.
NS records for this zone are defined at syncreon.com.
Question and response
Question
dig mailus1.syncreon.com. NS
Answer
The response has no answer records.
Authority
syncreon.com. 3600 SOA ns1.syncreon.com. hostmaster.syncreon.com. 1507 900 600 604800 3600
Additional
. 0 OPT ; payload 1224, xrcode 0, version 0, flags 0