S/MIME isn't support in this view

Dear Chou,

Good day, and thank you for reaching out to the Q&A Forum. From your description and my research, the message"S/MIME isn't supported in this view" usually means that the sender sent you a digitally signed or encrypted S/MIME message, but the current Outlook view cannot process it correctly.

As a forum moderator, I am not able to access your account or delve into the backend systems to diagnose and fix this for you. My role here is limited to providing general guidance and solutions for you to implement on your side. Please try the following steps to see if it helps:

1.Open in a separate window

Double-click the message in the message list so that it opens in its own window.

Some Outlook views may show the S/MIME warning while a separate message window can display the protected content correctly. Please note that this will not help if the message is encrypted and the required certificate or private key is unavailable on your device.

2.Install the sender's certificate from a signed email

When you receive a signed email, Outlook provides a feature to install the corresponding encryption certificate on your device (if the certificate is available). Once installed, it can be used to send encrypted email to the same sender and to help decrypt future messages.

1. Open a signed email.
2. Select the digital signature icon in the reading pane.
3. Select Install.

3.Test in classic Outlook

If you are currently using new Outlook desktop, try switching back to classic Outlook by toggling the New Outlook switch at the top-right corner, then try opening the same mailbox and message there.

If the attachment opens in classic Outlook but not in new Outlook / OWA, this points to a new Outlook compatibility or configuration issue rather than a damaged attachment.

4.Contact your school IT / help desk

If the message fails to open in both new and classic Outlook, since this is a school-managed account, the most appropriate next step is to contact your school IT / help desk. S/MIME requires organization-side configuration, and for encrypted messages, the recipient must have the corresponding certificate and private key installed on their device. Your IT team can:

• Confirm whether S/MIME is enabled/configured correctly for your mailbox.
• Help you install or enroll the required S/MIME certificate.
• Verify whether the sender's message is signed, encrypted, or both.

If you don't know who your IT administrator is, please refer to this article: How do I find my Microsoft 365 admin? - Microsoft Support 

For references:

Configure S/MIME For Windows | Microsoft Learn

Configure S/MIME in Exchange Online | Microsoft Learn

I hope this information is helpful. Please try these steps and let me know how it goes. If you have any questions or need further assistance, please feel free to share them in the comments so I can continue to support you. Thank you for your patience and understanding. I look forward to your reply.

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