mta.feedback.ul.com has no MX records.
Question and response
Question
dig mta.feedback.ul.com. MX
Answer
The response has no answer records.
Authority
ul.com. 1800 SOA carlos.ns.cloudflare.com. dns.cloudflare.com. 2396292669 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0