Problem to send S/MIME email Outlook 365

Question

Hello,

I'm using Windows 11 Enterprise (build 22000.675) + Office365 (Version 2204 Build 16.0.15128.20210). I have problem with S/MIME. I installed new PC (before I have W10+O365 without problem), exported smime certificate with private key from old computer, imported to new computer. Then installed certificate in outlook in Trust center:

But I have greyed Hash Algorithm and Encryption Algorithm. When I try to send email, outlook will display warning message: "The operation failed. The messaging interface have returned an unknown error. If this problem persists, restart Outlook." and does not send email.

I found some same questions from another users, but no solution. I tried to delete and create outlook profile, remove certificate and re-import, created self signed smime certificate, but nothing work.

Answer 1

Hi @DanielSKK ,

Thanks for your feedback above which shared more information and glad to know that your issue is resolved now! Since our forum has the policy that The question author cannot accept their own answer. They can only accept answers by others, and according to the scenario introduced here: Answering your own questions on Microsoft Q&A

I would make a brief summary of this post so that other forum members could easily find useful information here:

[Activating lagged copies - Summary]

Issue Symptom:
Trying to send a S/MIME signed message fails and got error: "The operation failed. The messaging interface have returned an unknown error. If this problem persists, restart Outlook"

Solution:
Delete the registered provider from the registry, i.e. the key
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Cryptography\Providers\AMD Provider].
After that, the PC must be rebooted.

Reference Links:
https://answers.microsoft.com/en-us/outlook_com/forum/all/outlook-20192016-trying-to-send-a-smime-signed/de792f65-2e6a-43a1-ac43-10673de75fca?page=2

You could "Accept Answer" for this summary to close this thread, and your action would be helpful to other users who encounter the same issue and read this thread. Thanks for your understanding!

Answer 2

Hi @DanielSKK ,

Welcome to our forum!

In order to verify, could you provide some related information for better research?

• What type of account are you using? Is it a Google account? Based on my search, I have found a known issue that mentioned this error: The operation failed error when you send email messages in Outlook
  In this article, which indicates that the issue occurs when a Google Apps Sync for Outlook account and an Exchange Server account are configured in the same Outlook profile. To workaround, you need to configure the Google Apps Sync for Outlook account in one profile and the Exchange Server account in another profile.
• How did you create a new profile? I'd suggest a new profile created from Control Panel > Mail > Show Profiles , then add your account.
• Besides, given that you have installed the S/MIME Certificate on a new PC, so you can check if you have installed it correctly, here is an article with detailed steps for you reference.
  (Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.)

If the issue resists, get back to our forum for more help.
I look forward to hearing from you.

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Answer 3

Certificate was correctly installed. I tried some other certificates from another authorities (not only from our private), I tried self-signed S/MIME too, but it is still same. My colleague tried other certificates too, but nothing happend.