mx.postimessaging.net has no CNAME records.
Question and response
Question
dig mx.postimessaging.net. NS
Answer
The response has no answer records.
Authority
postimessaging.net. 5143 SOA namesurfer.inet.fi. hostmaster.telia.fi. 2025092315 28800 7200 3456000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0