mx2.limestonenetworks.com has no AAAA records.
Question and response
Question
dig mx2.limestonenetworks.com. AAAA
Answer
The response has no answer records.
Authority
limestonenetworks.com. 2560 SOA ns1.limestonenetworks.com. noc.limestonenetworks.com. 1772213302 16384 2048 1048576 2560
Additional
. 0 OPT ; payload 1680, xrcode 0, version 0, flags 0