relay.spamshield.io has no MX records.
Question and response
Question
dig relay.spamshield.io. MX
Answer
The response has no answer records.
Authority
spamshield.io. 300 SOA ns1.io-servers.com. admin.io-servers.com. 2023080100 86400 7200 3600000 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0