Outlook The Security Certificate Was Issued By A Company You Have Not Chosen To Trust Apr 2026

It sits there, staring back at you, blocking your calendar, your email flow, and your sanity. Do you click "Yes," "No," or "View Certificate"? And more importantly, should you be worried?

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?

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. It sits there, staring back at you, blocking

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

If you manage Microsoft Outlook in a corporate environment, or even just use it for business email, you have likely stared at that dreaded pop-up: Outlook (and Windows) maintains a list of "Trusted

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?"

Decoding the Outlook Nightmare: "The Security Certificate Was Issued by a Company You Have Not Chosen to Trust" The domain names don’t match

Your company uses Microsoft Exchange Server on-premise. The server presents a self-signed certificate or one issued by your internal Microsoft PKI (Certificate Services). Your personal computer doesn't know your company's internal CA. Outlook sees "Issued by: Contoso-Internal-CA" and thinks, "I don't know Contoso. I never agreed to trust them."

Stay secure. Stay skeptical. And for the love of all that is holy, stop using self-signed certificates for production Exchange servers.

Let’s cut through the noise. This isn't just a random glitch; it’s a critical security mechanism waving a red flag. Here is a deep dive into what causes this error, the genuine risks involved, and the surgical steps to fix it—without compromising your network security. First, understand what Outlook isn’t saying. It is not saying the connection is unencrypted. It is saying, "I have a valid mathematical lock, but I don’t recognize the locksmith who made it."

"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."