Cloudflare email adds _dc-mx even when modified

Hi. I’m getting email deliverability issues to Microsoft Exchange. Here is the return error (I have removed my domain names from the below examples):

That user is a new Exchange test account that I have set up and it accepts other emails from domains including Gmail, Hotmail etc.
For info, I have also had problems sending to older Microsoft Exchange accounts too, but bizarrely not Live.co.uk or Hotmail addresses.

I have gone through extensive MXToolbox testing and have SPF, DKIM, DMARC correctly set up on my account and other recipients receive my emails fine.

I think that my problem is probably that I have the _dc-mx.12345678.mydomain as a hostname that resolves to my server’s IP address.

I have looked into this and the only resolution I can see on Cloudflare is to set these records:

MX mydomain mail.mydomain
A mail 192.168.0.2 <= (My server IP)

I have been using this (for several months) but with the same problem.

My actual mail server is on the same Server IP as my domain but it has a different name:
server1.mainservername

I have also tried setting just the MX record to:
MX mydomain mainservername
and not using an A record for mail. This removes the _dc-mx issue but the emails also get rejected the same way.

There is no orange cloud on anything except my domain and the www Cname.

I have tested my server IP and domain against the Microsoft ‘unblock’ form and it says neither is being blocked.

Any solutions or ideas are very welcome as I’m tearing my hair out at this point.

Yes, Cloudflare does this when you point your MX record at a proxied hostname, because a proxied hostname can’t work for email. Unfortunately, _dc-mx is not a valid DNS hostname, so it will result in some mail failing to be delivered.

Basically, you need to have an MX record pointed at a hostname (A record) that is not set as proxied on Cloudflare. (An MX record must not point directly to an IP address.)

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Yes, that’s what I have but it still gives me the _dc-mx hostname.

I imagine this is because my mail server is on another domain (still the same IP address though). So how to fix that?

There’s no problem with an MX record pointing to a different domain. If you can share the domain name it would be helpful.

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