alpha1.rdrhost.com has no MX records.
Question and response
Question
dig alpha1.rdrhost.com. MX
Answer
The response has no answer records.
Authority
rdrhost.com. 1800 SOA ns.gransy.com. root.gransy.com. 2772118360 86400 900 1209600 1800
alpha1.rdrhost.com. 1800 NSEC alpha2.rdrhost.com. A RRSIG NSEC
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0