Most emails deliver fine - certain senders (possibly with one hosting company only) seem to get above error message when trying to email me.
My Cloudflare DNS settings have CNAME mail westkerry.ie DNS only (not proxied)
The DNS “_dc-mx.0902b09372c2.westkerry.ie” is resolving for me but according to service like dnschecker there’s few servers not resolving it correctly (Mexico + Denmark).
What can I do to fix this?
I’m 99% sure there’s some issue the way configured the Cloudflare DNS settings.
You have your MX record pointed at a DNS entry that is proxied through Cloudflare. This won’t work because the Cloudflare proxy only works for web traffic. Your MX record should be pointed at an A record that is set as “DNS Only” in Cloudflare.
Because it’s pointed at a record that can’t work for email, Cloudflare automatically generates this MX record starting with _dc-mx. Unfortunately, this is not a valid DNS hostname, and will result in some email being lost in exactly the manner you describe.
Probably, in the Cloudflare DNS settings, you have your MX record pointed at your root domain name, which is proxied. What you need to do is point an A record at your mail server (something like mail.westkerry.ie), and ensure that this record has the Cloudflare proxy turned off. Your MX record should point at that A record, not at a record that is proxied through Cloudflare.