gamma.host-on.net has no MX records.
Question and response
Question
dig gamma.host-on.net. MX
Answer
The response has no answer records.
Authority
host-on.net. 86400 SOA a.ns14.net. do-not-reply.host-on.net. 2026011000 43200 7200 1209600 86400
Additional
. 0 OPT ; payload 1220, xrcode 0, version 0, flags 0