Keeping Confidential Outlook Email Private

Privacy and Protection Might Not be Enough

MVP Ingo Gegenwarth’s post about Outlook and private items is a good example of the problems which arise when user assumptions running into software limitations. The assumption is that if you mark an item as private, only you can see its contents. The limitation is that it depends on clients containing code to respect private items. Some do, and some don’t, much to the chagrin of users when they find out.

Delegate Access to Protected Email

Similar confusion exists around protected email which arrives in a user mailbox and is read by a delegate. Email protected by a sensitivity label uses rights management to know what a user can do with the content. If they don’t have the right to view the encrypted content, the mail client shouldn’t open the message. But if someone has delegate access to a user or shared mailbox, they might be able to read protected messages. It all depends on the client used and the rights assigned in the sensitivity label.

For instance, here’s an example where a protected message arrives in a mailbox. The delegate (full mailbox access) can read the protected message with OWA (left), but not with Outlook desktop (right). They can also read the message with Outlook mobile if they add their delegate account there.

Delegate access to Outlook email works with OWA but not desktop
Figure 1: Delegate access to Outlook email works with OWA but not desktop

Change Coming for Some Outlook Clients

In their FAQ for protected email, Microsoft says:

Is delegated access supported with opening encrypted messages? Even if a delegate has full access to another user’s mailbox?

Delegated access of encrypted mail is supported in Outlook on the web, Outlook for Mac, Outlook for iOS, and Outlook for Android. Outlook for Windows does not support delegated access.”

A change described in Microsoft 365 roadmap item 88888 appears as if it will help. The item says:

“Outlook will provide consistent access control on protected emails for 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 setting to block the owner’s protected email access which covers ad-hoc encrypted email as well as email with protected MIP sensitivity labels.”

According to the roadmap, we will see this change in April 2022. However, it only applies to OWA, Mac, iOS, and Android. Outlook for Windows remains an outlier. And that’s the problem because Outlook for Windows is often the client of choice for administrative assistants who process email on behalf of others.

Protecting Confidentiality

Is there anything that can be done in the situation where the organization uses sensitivity labels to protect confidential email and documents and want to be sure that delegates cannot access this material? Well, you could remove OWA and Outlook Mobile access from delegate accounts to force them to use Outlook desktop, but that’s probably not realistic.

Instead, an old technique from on-premises Exchange might be useful. For executives who need the assurance that delegates cannot access protected email, you could create two accounts with mailboxes. Let’s take the example of the CEO. They would have:

  • A primary mailbox accessed by the delegate to manage inbound email and the calendar. The mailbox appears in the GAL and is accessible to anyone in the organization (or maybe not, as the case demands).
  • A hidden mailbox which only the owner can access. This mailbox is not listed in the GAL and is limited so that only certain people can send email to it. This mailbox is used for protected or other confidential email, so the rights assigned in sensitivity labels grant access to the hidden mailbox instead of the primary mailbox.

A certain amount of configuration to make sure that the two accounts work as planned. However, if protected email is sent to the hidden mailbox and only the owner of that mailbox accesses the email, there’s no chance that the delegate can see confidential material.

Yes, this is a pain. Delegate access to protected email should work better with Outlook for Windows. Let’s hope that Microsoft moves on this point soon. Perhaps it’ll be an example of their One Outlook strategy of bringing OWA features to Outlook desktop.

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