mail.centex.net has no MX records.
Question and response
Question
dig mail.centex.net. MX
Answer
The response has no answer records.
Authority
centex.net. 900 SOA ns1.centex.net. please_set_email.absolutely.nowhere. 2010531303 10800 3600 2592000 900
Additional
. 0 OPT ; payload 1220, xrcode 0, version 0, flags 0