121.55.192.guam.net has no MX records.
Question and response
Question
dig 121.55.192.guam.net. MX
Answer
The response has no answer records.
Authority
121.55.192.guam.net. 3600 SOA NS.guam.net. HostMaster.ns.guam.net. 2010080500 3600 3600 3600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0