M365 Changelog: (Updated) block delegates or shared mailbox members from accessing protected messages in Outlook

MC389620 — Updated September 28, 2022: Microsoft has updated the rollout timeline below. Thank you for your patience.

Outlook will provide consistent access control on protected emails (Protected by MIP Sensitivity labels, or RMS protected emails) for Microsoft 365 delegates and shared mailbox members. For delegates or shared mailbox members, when they have full access of the owner’s mailbox but are not allowed to read encrypted email, Outlook will have a new cmdlet setting to block the owner’s protected email access which covers ad-hoc encrypted email as well as email with protected MIP sensitivity labels.

This message is associated with Microsoft 365 Roadmap ID: 88888

When this will happen:

• Preview: Microsoft will roll out the preview in early June
• Standard: Microsoft will begin rolling out in early July and expect to complete by early October (previously late August)

How this will affect your organization:

Based on customer feedback, Microsoft is introducing new Get/Set/Remove-MailboxIRMAcess cmdlets that provide admins with more granular access control of encrypted content, including in scenarios where delegates or shared mailbox members have FullAccess to the shared mailbox

Microsoft will introduce new Get/Set/Remove cmdlets which tenant admins to use to limit delegate access to RMS messages at mailbox level.

• Check who is blocked from accessing mailbox owner’s encrypted messages:

Get-MailboxIRMAccess -Identity <MailboxIdParameter> -User <SecurityPrincipalIdParameter>

• Blocked a user from reading encrypted messages in a shared or delegated mailbox:

Set-MailboxIRMAccess -Identity <MalboxIdParameter> -User <SecurityPrincipalIdParameter> -AccessLevel <Block>

• Remove a user from the block list and allowing them to read encrypted mail:

Remove-MailboxIRMAccess -Identity <MalboxIdParameter> -User <SecurityPrincipalIdParameter>

After any of the above mailbox settings are changed, the Outlook client must be restarted.

Parameter definitions:

• -Identity: The target mailbox. You can use any value that uniquely identifies the mailbox.
• -AccessLevel: Specifies what delegates can do with IRM-protected messages in the specified mailbox. Currently, Microsoft only supports “Block.”
• -User: Specifies the delegate or shared mailbox member who is blocked from reading IRM-protected messages in the mailbox or shared mailbox. The user’s login ID must be used.

Once delegate is blocked to view the owner mailbox’s protected email, the delegate will see the following when they trying to open the protected mails

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Or Shared mailbox member is blocked to view the mailbox’s protected email, the login user will see the following when they trying to open the protected emails.

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What you need to do to prepare:

If you do not do any cmdlet settings, there will be no impact on your existing delegate or shared mailbox protected message reading experience. But if you choose to block some of the full access delegate or shared mailbox members to read the protected email, you could configure through the cmdlet above.

Additional information

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