cust-64.79.155.0.switchnap.com has no MX records.
Question and response
Question
dig cust-64.79.155.0.switchnap.com. MX
Answer
The response has no answer records.
Authority
switchnap.com. 3600 SOA ns1.switch.com. hostmaster.switch.com. 2026012201 10800 900 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0