ext-relay.a1.group has no MX records.
Question and response
Question
dig ext-relay.a1.group. MX
Answer
The response has no answer records.
Authority
a1.group. 3600 SOA dns3.a1.net. domainadmin.a1.net. 2026020500 10800 3600 1814400 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0