aspmx.sailthru.com has no NS records.
NS records for this zone are defined at sailthru.com.
NS records for this zone are defined at sailthru.com.
Question and response
Question
dig aspmx.sailthru.com. NS
Answer
The response has no answer records.
Authority
sailthru.com. 180 SOA ns10.digicertdns.com. dns.digicertdns.com. 2009010497 43200 3600 1209600 180
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0