dns-01.ultradns2.org has no MX records.
Question and response
Question
dig dns-01.ultradns2.org. MX
Answer
The response has no answer records.
Authority
ultradns2.org. 300 SOA pdns1.ultradns.net. domains.vercara.com. 2022071124 300 900 86400 300
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0