I have Outlook 2016/365, and we just started having this problem- Our DNS was compromised and I had to rebuild the zones from scratch. I get email, and everything seems to work... except something is still looking in the wrong place, and I don't know what. We get a nuisance pop-up when starting Outlook about a cPanel certificate - the CA is valid, the certificate is expired, and the certificate contains a valid name. This certificate is not on our Exchange servers- I have verified that the only certificates not self-signed (We are using on-prem Exchange 2013) on our Exchange servers are GoDaddy certificates. Our mail and MX records point to our public IP, and I have been using mxToolbox to verify those plus other DNS records. The autodiscover record has been a CNAME pointed to our domain's mail record, and I recently changed it to an A record pointing at this IP address. No change. I also have the SRV pointed to the mail record on the domain using port 443. The certificate message appears right when I start Outlook- Any idea which record is wrong? Any idea how to troubleshoot?