Enable Digital Signature and Encryption with S/MIME through Outlook on the Web

Brittany Hutman 5 Reputation points
2024-08-01T18:10:17.4833333+00:00

I work at a company that has a Hybrid environment with M365/Azure. We use a third-party Certificate issuing Authority to issue digital signing and encryption certs. We would like to allow users to encrypt/sign emails through Outlook on the web from laptops that are domain joined but do not have the Outlook App.

I am able to get the S/MIME extensions to install fine on Edge/Chrome, and users can now read the encrypted/signed emails but still are unable to actually send encrypted/signed emails. The SMIME Controller is downloaded. The error comes back as "The certificate used to sign this message isn't trusted by your organization."

I've exhausted several hours trying to run down a solution for using local AD, Entra ID, M365 Admin Center, and Intune to accomplish this and can't find anything that is a start to finish guide.

Help on this would be much appreciated, if it's even a thing that can be done.

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