As a quick fix add the following static FWD lines to your router:
/ip dns static
add forward-to=159.148.147.201 regexp=".*\\.sn\\.mynetname\\.net\$" type=FWD
add forward-to=159.148.172.251 regexp=".*\\.sn\\.mynetname\\.net\$" type=FWD
And flush the DNS cache !
This forwards any query for *.sn.mynetname.net to DNS servers: 159.148.147.201 or 159.148.172.251