Error When Opening Encrypted Emails or Encrypting Messages/Documents

Question

Hello Microsoft Support,

I'm writing because I'm having trouble with email and document encryption in Microsoft Office on my Mac. Every time I try to open an encrypted email or encrypt something myself, I get an error. The details are below:

• Correlation Id: [Moderator note: personal info removed]
• Timestamp: 2025-12-02T09:17:53.000Z
• DPTI: [Moderator note: personal info removed]
• Error Message: The authority we are trying to validate is not a trusted authority.
• Tag: 6xuaf
• Code: 0

A bit about my setup:

• I'm using a new MacBook Pro with an M3 chip.
• macOS version is 14.6.1 (23G93).
• My Office version is 16.103.2 (25112216) for Mac.

The frustrating part is that this isn't just happening to me - the same exact problem is occurring on seven new MacBooks in our team, all with the same specifications and software versions. We've all checked that our systems and certificates are up to date, but the error keeps appearing.

Could you help us figure out how to fix this? A few specific questions I have:

1. Do we need to update or reinstall specific certificates on our Macs?
2. Should we change any settings for trusted certification authorities in Office or macOS?
3. Are there any diagnostic steps we should run in Outlook to gather more useful logs for you?

Let me know what other information you might need from us to investigate this. We'd really appreciate your help getting this resolved for our team.

Thanks in advance,

Answer 1

Please note that our forum is a public platform, and we will modify your question to hide your personal information in the description. Kindly ensure that you hide any personal or organizational information the next time you post an error or other details to protect personal data.

Hi Daniil Poldyaev

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

May I ask you are using Self-Signed certificate or CA-Signed certificate (public or private)?

If you are using Self-Signed certificate, each client must manually trust the certificate or its issuer.

To do that, open Key Chain on Mac, Import Items to add the certificates into the System keychain. Then expand Trust > For When using this certificate, choose Always Trust.

If you are using public CA-Signed certificate, it is already trusted by most operating systems and browsers.

For private CA, it requires installing the CA’s root certificate on client devices.

You need to trust the certificate just like self-signed Certificate.

Some related articles:

Send a digitally signed or encrypted message for Mac - Microsoft Support

Request a certificate from a certificate authority in Keychain Access on Mac - Apple Support

Change the trust settings of a certificate in Keychain Access on Mac - Apple Support

Note: Microsoft is providing this information as a convenience to you. These sites are not controlled by Microsoft, and Microsoft cannot make any representations regarding the quality, safety, or suitability of any software or information found there. Please ensure that you fully understand the risks before using any suggestions from the above link.

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