smtp.coconline.nl has no MX records.
Question and response
Question
dig smtp.coconline.nl. MX
Answer
The response has no answer records.
Authority
coconline.nl. 617 SOA ns2.argewebhosting.com. plesk.cldin.eu. 2025121608 10800 3600 604800 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0