mailfilter03.cobytes.io has no MX records.
Question and response
Question
dig mailfilter03.cobytes.io. MX
Answer
The response has no answer records.
Authority
cobytes.io. 86400 SOA ns1.cobytes.io. hostmaster.cobytes.io. 2026020601 14400 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0