smtp-relay.colocenter.nl has no MX records.
Question and response
Question
dig smtp-relay.colocenter.nl. MX
Answer
The response has no answer records.
Authority
colocenter.nl. 3600 SOA ns1.colocenter.nl. hostmaster.colocenter.nl. 2025040247 3600 3600 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0