mx.ALTO.FR has no NS records.
NS records for this zone are defined at ALTO.FR.
NS records for this zone are defined at ALTO.FR.
Question and response
Question
dig mx.ALTO.FR. NS
Answer
The response has no answer records.
Authority
ALTO.FR. 86400 SOA NS.ALTO.ORG. HOSTMASTER.LYNXALTO.COM. 2014082208 28800 7200 604800 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0