Outlook The Security Certificate Was Issued — By A Company You Have Not Chosen To Trust

Never click "Yes" to this error on a public network. Always verify the "Issued by" field. When in doubt, call your IT helpdesk and ask, "Did you guys recently roll out a new internal root CA?"

Outlook tries to connect to mail.company.com , but the server’s certificate is actually for exchange01.internal.local . The domain names don’t match. Even if the certificate is from VeriSign, the mismatch triggers the same error because the "company" (the subject of the cert) doesn't align with the URL. Never click "Yes" to this error on a public network

Stay secure. Stay skeptical. And for the love of all that is holy, stop using self-signed certificates for production Exchange servers. The domain names don’t match

If the answer is "No," Outlook slams the brakes. This usually happens in three specific scenarios: Stay skeptical

Outlook (and Windows) maintains a list of "Trusted Root Certification Authorities." These are global companies like DigiCert, GlobalSign, or Let's Encrypt. When a certificate is presented, Outlook checks: Is the issuer on my trusted list?

Decoding the Outlook Nightmare: "The Security Certificate Was Issued by a Company You Have Not Chosen to Trust"

"The security certificate was issued by a company you have not chosen to trust. View the certificate to determine whether you want to trust the certifying authority."