External Destination Verification

If a warning appears which indicates that your DMARC record has a problem along these lines, "external destination verification", you have pointed at least some portion of your reporting to a destination which is not correctly configured to receive those messages.  

We have a very good article explaining the problem and situation here, please read it:

https://dmarcian.com/what-is-external-destination-verification/

Sometimes the problem is simply that you have incorrectly transcribed the dmarcian.com reporting address; carefully compare what is recommended in the 'Add DMARC Record' area to what is actually in your DMARC record.

To note: there is at least one large DMARC reporter which does not adhere to this important security consideration, so in some cases an unconfigured reporting destination will still get *some* portion of reporting - you'll still have to fix the problem because "some" is not "all" or even "most", usually.