ContributionsMost RecentMost LikesSolutionsCXDNS Error and blocking my outbound IP address 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. Re: Blocked IP? I have the exact same problem with a Windows based machine using Outlook 360. Same errors except it is a different IP address listed. Mine says it is 8.40.179.163 which is not an IP I am aware of. I do not have an IT department as I am at a residence. I am using a different ISP other than Cox to access the internet but I am paying Cox 9.99 a month to keep my email address and data. This problem started about the last week in April. I checked with my ISP, Vyve Broadband, and they are telling me that Cox is failing the DNS from them. Please resolve this issue and allow.