sitebuilder-mail-out.dynadot.com has no MX records.
Question and response
Question
dig sitebuilder-mail-out.dynadot.com. MX
Answer
The response has no answer records.
Authority
dynadot.com. 1800 SOA magdalena.ns.cloudflare.com. dns.cloudflare.com. 2398341826 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0