cust.keyyo.net has no MX records.
Question and response
Question
dig cust.keyyo.net. MX
Answer
The response has no answer records.
Authority
cust.keyyo.net. 300 SOA cust.keyyo.net. mail.cust.keyyo.net. 2019101701 300 300 1700000 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0