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In late April 2019 my outbound email stopped working from my cox account. I am using Outlook 365 and have verified that my settings are unchanged from when it was working and matches Cox email settings. I have contacted Cox support on the phone and they said it is my ISP's problem. I contacted my ISP and they say that Cox is failing my IP address on a Reverse DNS lookup. Based upon the number of other cox customers that are complaining of the same problem, I suspect that something changed in late April that has affected DNS lookups. How do I get Cox to accept my ISPs IP assignment? I have checked to verify that it is not flagged by spamhaus and it is safe.
The error message I get states that my IP is blocked and that the error code CXDNS.