451be600.cst.lightpath.net has no MX records.
Question and response
Question
dig 451be600.cst.lightpath.net. MX
Answer
The response has no answer records.
Authority
lightpath.net. 86400 SOA authns1.cv.net. abuse.cv.net. 2013414889 7200 600 604800 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0