s/mime sign cannot be verified when viewing in secondary account

Ralf 0 Reputation points
2026-02-20T05:36:05.8766667+00:00

We are using shared mailbox and I'm getting this error "s/mime sign cannot be verified when viewing in secondary account" but my colleagues are not getting this error.

Any fix for this issue? Thank you

Outlook | Windows | New Outlook for Windows | For business
0 comments

2 answers

Sort by: Oldest
Most helpful Newest Oldest

  1. AI answer

    2026-02-20T05:36:16.0533333+00:00

    The error "S/MIME sign cannot be verified when viewing in secondary account" typically occurs due to issues with the digital certificates associated with the shared mailbox or the configuration of the Outlook profile. Here are some steps you can take to troubleshoot and potentially resolve the issue:

    1. Verify Digital Certificates: Ensure that the digital certificate used for signing the emails is correctly installed and recognized in the Outlook profile associated with the shared mailbox. You may need to check if the certificate is valid and not expired.
    2. Add to Contacts: If the sender of the signed email is not in your contacts, try adding them. Open the signed email, right-click on the sender's name in the "From" line, and select "Add to Outlook Contacts". Make sure to verify the public key certificate for the contact.
    3. Check Address Book Policies: If your organization uses multiple Address Book policies, ensure that the shared mailbox and the user accounts are configured correctly within the same policy. Avoid creating distribution lists that span multiple Address Book policies, as this can lead to verification issues.
    4. Outlook Profile Configuration: Sometimes, the Outlook profile may not be configured correctly. Consider removing and re-adding the shared mailbox to your Outlook profile to refresh the settings.
    5. Registry Settings: If you have administrative access, you may want to check if the registry settings for S/MIME are configured correctly, especially if other users are not experiencing this issue. You can refer to the registry settings that allow users to select their signing certificate if applicable.

    If these steps do not resolve the issue, it may be beneficial to consult your IT department or Microsoft support for further assistance.

    References:

    AI-generated content may be incorrect. Read our transparency notes for more information.

    Was this answer helpful?

  2. Kai-Ex 1,585 Reputation points Microsoft External Staff Moderator
    2026-02-20T06:38:58.6933333+00:00

    Dear Ralf ,

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

    When you open an S/MIME‑signed email from a shared mailbox, Outlook must verify the digital signature using the certificate installed on the local machine profile of the user who is reading the email. This is a known Outlook/Exchange behavior when using shared mailboxes with S/MIME. 

    Kindly following these steps to help you resolve the issue: 

    1. Set up S/MIME certificate 

    Kindly request your IT Admin to follow this article to set up S/MIME certificate: Set up Outlook to use S/MIME encryption - Microsoft Support. 

    1. Enable the S/MIME add‑in 

    Settings > Mail > S/MIME 

    Install the S/MIME extension if required. 

    Note: If the add‑in is missing or disabled, Outlook cannot verify signatures. 

    1. Remove and re-add the shared mailbox 

    Remove your automapping permissions 

    Add the shared mailbox manually by following these steps: Open and use a shared mailbox in Outlook - Microsoft Support. 

    1. Check account’s permission 

    Your administrator should verify that your account has: 

    Full Access 

    Read and Manage S/MIME certificates 

    Note: Please understand that as a forum moderator, my primary goal is to provide helpful guidance and support through general troubleshooting steps. While I don’t have access to internal systems or test devices required to resolve backend/account issues, I truly appreciate your understanding of these limitations.  

    Thank you for choosing Microsoft, and I am looking forward to your response. If anything is unclear, please don’t hesitate to reach out to me. 

     If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have any extra questions about this answer, please click "Comment."    

    If you want to receive the related email notification for this thread, please follow the steps in our documentation to enable e-mail notifications.

    Was this answer helpful?

Your answer

Answers can be marked as 'Accepted' by the question author and 'Recommended' by moderators, which helps users know the answer solved the author's problem.