ciscoaisummit.com has no MX records.
Question and response
Question
dig ciscoaisummit.com. MX
Answer
The response has no answer records.
Authority
ciscoaisummit.com. 120 SOA hns001.sjc03.webex.com. csg-ia.cisco.com. 20 10800 1800 2419200 120
Additional
. 0 OPT ; payload 1220, xrcode 0, version 0, flags 0