How-to Import certificates in OWA for 365 tenant users to sign and encrypt messages and choose which certificate to use on each email.

Question

How-to Import certificates in OWA for 365 tenant users to sign and encrypt messages and choose which certificate to use on each email.

Rita Rita 115

Hello

Please i need your help on this issue.

How-to Import certificates in OWA for 365 tenant users to sign and encrypt messages and choose which certificate to use on each email.

we want help on how to setup and import certificates in owa, so users can sign and encrypt their emails. All users have a personal certificate and some of them are using a shared mailbox certificate. we want to be able to use the appropriate certificate each time.

Note: they are using their personal windows devices, so the pcs are not Entra registered or joined.

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Answer 1

Hin-V 7,060 Microsoft External Staff Moderator

Hi @Rita Rita

Thank you for posting your question in Microsoft Q&A.

To better assist you with importing certificates and setting up email signing and encryption in Outlook Web App (OWA) for Microsoft 365, we need some additional details about your setup and requirements. Could you provide additional information for the following question:

Are you specifically using S/MIME for email signing and encryption, or are you using a different method?

Are the certificates for shared mailboxes separate from personal certificates? If so, how are they being distributed to users?

I have found some relevant articles, and I hope this helps:

Set up Outlook to use S/MIME encryption - Microsoft Support
Configure S/MIME in Exchange Online | Microsoft Learn
I will be waiting for your response. If you need further assistance, please let us know.

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

Hin-V 7,060 Reputation points Microsoft External Staff Moderator

2025-10-22T07:49:36.94+00:00

Hi @Rita Rita

I hope you are doing well.

Have you had a chance to check the replies provided?

Any update would be appreciated.
Rita Rita 115 Reputation points

2025-10-22T13:58:36.4866667+00:00

Hello Hin-V

Thank you for your reply.

we are using S/MIME certificates issued by Actalis, with the correct email protection EKU.

The Certificates are installed on each user’s device in the appropriate Current User > Personal store.

The certificates are in .P12 format and are not currently exportable by end users.

The Users access email via Microsoft Edge and have not yet installed the S/MIME control/extension.

We are using shared mailbox certificates, manually installed on each device, and wish to support sending signed/encrypted emails from either the user’s personal mailbox or the shared mailbox—switching the certificate based on the sender.

We would like to switch certificates based on sender address (personal vs shared mailbox) and ideally store the shared certificate in OWA or deploy it automatically to unmanaged devices.

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How-to Import certificates in OWA for 365 tenant users to sign and encrypt messages and choose which certificate to use on each email.

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