mail.sensenet.com has no NS records.
NS records for this zone are defined at sensenet.com.
NS records for this zone are defined at sensenet.com.
Question and response
Question
dig mail.sensenet.com. NS
Answer
The response has no answer records.
Authority
sensenet.com. 600 SOA ns1-01.azure-dns.com. support.sensenet.com. 2012042273 28800 14400 1209600 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0