smtp15.validname.com has no MX records.
Question and response
Question
dig smtp15.validname.com. MX
Answer
The response has no answer records.
Authority
validname.com. 600 SOA ns1.namebay.com. admin.validname.com. 2026011202 1200 180 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0