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

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."

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?" Your company uses Microsoft Exchange Server on-premise

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. Outlook sees "Issued by: Contoso-Internal-CA" and thinks, "I

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? When in doubt, call your IT helpdesk and