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

Brittany Hutman 0

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.

Faery Fu-MSFT 18,831 Reputation points Microsoft Vendor

2024-08-02T08:26:44.87+00:00

Hi @Brittany Hutman ,

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.

Does this problem occur on both Edge and Google Chrome?

Can you provide a specific error screenshot?

Please note that S/MIME is only supported on Windows desktop devices for Outlook on the web, S/MIME isn't available in Outlook on the web on Mac, iOS, Android, or other non-Windows devices. More information, see: Encrypt messages by using S/MIME in Outlook on the web
Faery Fu-MSFT 18,831 Reputation points Microsoft Vendor

2024-08-06T05:30:14.5966667+00:00

Hi @Brittany Hutman ,

Is there have any update from you? If yes, please feel free to let us know.

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

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