Labeled and encrypted Mails in Shared Mailbox

Depending on the encryption configuration, it is not possible to open a message encrypted via a Sensitivity Label from a shared mailbox using Outlook New or Outlook on the Web. This results in an endless loop prompting the end user to open the message in a different context. However, selecting "Read the message" leads to the same recurring message. We discussed this topic in different cases but were not able to resolve the issue.

Below is a more detailed description of the problematic scenario:

Affected Clients:

• Outlook New (Windows & Mac), Outlook on the Web (presumably also Mobile)

Sensitivity Label Configuration:

• Active encryption
• Centrally predefined access permissions
• Permission assignment (e.g., Co-Owner) to individual users and/or groups

Identities:

Shared Mailbox:

• The user object is not included in the label’s permission assignment

Affected users (everyone):

• Have full access to the shared mailbox
• Are included as Co-Authors in the label’s permission assignment

Issue: The user sends a labeled email to the shared mailbox, to which they also have full access. For example, the same user then navigates to the shared mailbox to open the encrypted email. Instead of the message content, the typical notification indicating a protected/encrypted email is shown, offering a deep link to open the message in Outlook on the Web. However, selecting the "Read the message" link only opens the same notification again in the context of the shared mailbox, causing the end user to enter an endless loop of newly opened prompts/tabs.

Image of the Message: image.png

Known Workarounds:

• The email is displayed correctly in Outlook Classic
• The email can be moved or forwarded to the personal mailbox and opened there → However, this is not a sustainable process
• If the user object of the shared mailbox is added to the label’s permission assignment, the message can be opened without issue → However, there are discrepancies between users who are authorized for the mailbox and those who have access to labeled content

The workarounds outlined in the following articles could not resolve the issue:

• https://learn.microsoft.com/en-us/purview/ome-faq?view=o365-worldwide&preserve-view=true#can-i-open-encrypted-messages-sent-to-a-shared-mailbox
• https://learn.microsoft.com/en-us/troubleshoot/outlook/user-interface/encrypted-restricted-message-shared-mailbox

Many thanks and regards