mta1.ungapped.io has no MX records.
Question and response
Question
dig mta1.ungapped.io. MX
Answer
The response has no answer records.
Authority
ungapped.io. 3600 SOA ns1.loopia.se. registry.loopia.se. 1771459200 14400 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0