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

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?

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." 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?" This isn't just a random glitch; it’s a

If the answer is "No," Outlook slams the brakes. This usually happens in three specific scenarios: It is not saying the connection is unencrypted

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."