rcdn-mx-01.cisco.com has no MX records.
Question and response
Question
dig rcdn-mx-01.cisco.com. MX
Answer
The response has no answer records.
Authority
cisco.com. 1800 SOA ns1.cisco.com. postmaster.cisco.com. 1178812 7200 1800 864000 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0