mx.micrusero.com has no NS records.
NS records for this zone are defined at micrusero.com.
NS records for this zone are defined at micrusero.com.
Question and response
Question
dig mx.micrusero.com. NS
Answer
The response has no answer records.
Authority
micrusero.com. 3600 SOA dns.micrusero.com. hostmaster.micrusero.com. 1406341699 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0