Why I can't open an received encrypted mail after it was redirected?

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Why I can't open an received encrypted mail after it was redirected?

simon daixin 20

I'm a member of shared mailbox A (hereinafter referred to as A) and shared mailbox B (hereinafter referred to as B).

Mails to A will be automatically redirected to B.

Most mails are visible in B to me, except several encrypted mails.

Although these encrypted mails are visible to me in A, they are invisible in B.

Please advise. Thank you!

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Answer 1

Hi simon daixin,

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

From your description, it seems you're experiencing an issue with encrypted emails that are sent to Shared Mailbox A and automatically redirected to Shared Mailbox B. Just to clarify, is the problem that some encrypted emails are not appearing in Mailbox B at all, or that the emails do arrive but cannot be opened once they’re in Mailbox B?

If it's the first case, where certain encrypted emails are not successfully redirected and you’re an IT or Exchange admin, I recommend using message tracking to trace the delivery path and status of those messages.

For Exchange On-Premises, you can use PowerShell with the Get-MessageTrackingLog command:

Get-MessageTrackingLog -Start "06/17/2025 00:00:00" -End "06/18/2025 23:59:59" -Sender "******@domain.com"

You can further filter by -Recipients, -EventId, or -MessageSubject as needed. More details are available here: Search message tracking logs | Microsoft Learn

For Exchange Online, you can use Message Trace in the new Exchange Admin Center (EAC). More information for this feature, please check: Message trace in the new EAC in Exchange Online | Microsoft Learn

In my own testing, I created a rule to redirect emails between mailboxes and used Message Trace in EAC. The results showed that you can view the information of redirected emails in the message trace:

The original email has been successfully sent to the first mailbox. Next is the trace of the email redirected to the target mailbox:
The trace of the redirected email included detailed information explaining why the redirect failed (if applicable).

If you're facing the second scenario where encrypted emails are redirected but cannot be opened in Mailbox B. I suggest reviewing this article: Open encrypted and protected messages - Microsoft Support.

However, in order to provide better support, I also need to know what encryption method you are using for your email. If you are using Microsoft Purview Message Encryption for your emails, then I found this article: Define mail flow rules to encrypt email messages | Microsoft Learn

I hope this helps clarify the situation and provides a useful path forward. Feel free to reach out if we are misunderstanding or haven't reach out your main point, please provide us a screenshot so we can troubleshoot your request more effective.

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

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simon daixin 20 Reputation points

2025-06-26T01:10:53.51+00:00

Thank you for your reply. I have some comments below.

I can read the contents of the encrypted mails in Mailbox A.

The redirected rule works well. And I can see the encrypted mails in Mailbox B redirected from Mailbox A, but just can't read the content of the mails.

Sorry I do not know how the mails are encrypted, cause I'm not the sender of the mails.

I changed the redirect rule to forward rule on Mailbox A yesterday.

It seems the same problem.

I can see the encrypted mails in Mailbox B forwarded from Mailbox A, but still can't read them. When I open one of them, It seems that the mail was forwarded from Mailbox A, but without any content.

There is a button named "Read the message" instead. When I click the button a new web page will be opened. The same encrypted mail with a "Read the message" button is in the page. It loops.
Kudos-Ng 870 Reputation points Microsoft External Staff Moderator

2025-06-27T09:42:35.5133333+00:00

Hi simon daixin,
Thank you for providing the additional details.

From what you've described, it seems the sender is using S/MIME encryption for the email.

Regarding S/MIME, unfortunately we don’t have the necessary certificates or test environment to reproduce this scenario. However, based on the information I’ve gathered, here’s a brief overview of how S/MIME works from Email encryption in Microsoft 365 | Microsoft Learn article:

Both digital signatures and message encryption are made possible through the use of unique digital certificates that contain the keys for verifying digital signatures and encrypting or decrypting messages. To use S/MIME, you must have public keys on file for each recipient. Recipients must maintain their own private keys, which must remain secure. If a recipient's private key is compromised, they need to obtain a new one and redistribute their public key to all potential senders.

This means that if the sender is using S/MIME, the encryption is likely tied to the intended recipient’s certificate. Therefore, if the email is redirected or forwarded to someone else (like B), that person may not be able to decrypt the message unless they were originally specified as a recipient with a valid certificate.

You can read more about S/MIME here: Understanding S/MIME | Microsoft Learn

To confirm whether this is the case, I suggest asking the sender to send an encrypted email directly to B and see if it can be opened successfully.

Let me know how it goes or if you have any further questions!
simon daixin 20 Reputation points

2025-06-30T07:56:22.3066667+00:00

Hi Kudos,

Thank you for your reply. I think it's because of S/MIME encryption. I will try another method.

Thanks.
Kudos-Ng 870 Reputation points Microsoft External Staff Moderator

2025-06-30T09:02:42.9666667+00:00

Dear simon daixin
Thank you for getting back to us.

We are very happy to know that my answer helped you better understand on this issue.

If you found the initial response helpful in any way, it would be greatly appreciated if you could mark it as an “Accepted Answer”. This helps other in the community facing similar problems.
Thanks for your understanding

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Why I can't open an received encrypted mail after it was redirected?

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