Project Monarch “One Outlook” Build Leaks

And Microsoft Issues Block to Stop People Using Leaked Client

Update: Microsoft has now released a public preview of the Monarch client. You can download the preview if you are a member of the Office Insiders program. See this post for details. The preview version is not very different to the leaked software.

A leaked build of Microsoft’s “One Outlook” client emerged last week. It wasn’t very exciting because it’s what Microsoft described during sessions at the Ignite conference in September 2020. “Project Monarch” is making progress, but it’s not the kind of fundamental breakthrough redevelopment of Microsoft’s venerable email client that some anticipated.

What leaked is a version of the Outlook Web App (OWA) client currently available to Exchange Online users. The client is complete with links in the navigation bar to invoke Yammer and Bookings, and icons to start a Teams chat or fast access to To Do tasks (Figure 1).

The Project Monarch "One Outlook" client connected to my Exchange Online mailbox
Figure 1: The Project Monarch “One Outlook” client connected to my Exchange Online mailbox

Support for shared mailboxes, Microsoft 365 Groups, sensitivity labels, and calendar board views is included, as is full support for Microsoft Editor, tab completion of phrases (with some interesting hiccups), and so on. I was even able to open a public folder. One thing that’s missing is Loop components, which Microsoft plans (MC370366) for both OWA and Outlook for Windows this month.

The Project Monarch client is packaged as a Progressive Web App (PWA) with limited offline capabilities (some calendar and email information is available, but not item contents). You can sign into the client with an Azure AD account, but not a consumer Microsoft Services account.

Prettier OWA

In a nutshell, this Project Monarch build is a slightly prettier version of OWA. When it’s feature-complete, it’s easy to see how Microsoft will slip this client in to replace:

  • OWA in Exchange Online (Office 365).
  • OWA in
  • The basic Mail app in Windows 11.

Of course, each version of the client will have different capabilities, but they’ll all use the same basic framework, and that’s the important point.

Core Technologies

Three core technologies form the One Outlook framework (see this Ignite 2020 video):

  • OPX – OWA Powered Experiences (Figure 2): a method to allow other clients to consume features developed for OWA. A good example is how Outlook for Windows uses the OWA Room Finder. OPX depends on the WebView2 component, developed by the Edge team. WebView2 is also key to the Teams 2.0 client architecture.
  • Microsoft Sync Technology: the synchronization protocol currently used by the Outlook mobile (iOS and Android) and the Outlook for Mac clients to interact with Exchange Online. The word is that Outlook for Windows will eventually move away from MAPI over HTTP to use this protocol.
  • Augmentation Loop: a way to coordinate the services and data consumed by Outlook clients. Instead of Outlook building separate interfaces to plug new services into clients, they plug into the augmentation loop.

OWA Powered Experiences (OPX) (source Microsoft)
Figure 2: OWA Powered Experiences (OPX) (source Microsoft)

Synchronize My Mailbox

Offline working is the big gap that Microsoft must plug before replacing the Outlook desktop client is possible. For the last twenty years, Outlook has been able to synchronize a user’s entire mailbox using network smarts like drizzle-mode synchronization and priority threads. A replacement for Outlook desktop must be capable of sophisticated offline working, meaning that the client needs to be able to do more than basic send and receive of email. There’s no evidence of progress toward this goal in the leaked PWA.

Blocking the Leak

In response to the leak, Microsoft released MC376710 late on May 6 to say that “some users can access an unsupported early test version of the new Outlook for Windows.” The announcement appealed for customers to wait until Microsoft releases an official beta, promising more news about the beta “in the coming weeks.”

Microsoft also gave instructions about how to block mailboxes from synchronizing with the new Outlook. To do this, connect to Exchange Online with PowerShell and run the Set-CasMailbox cmdlet to block access, just like you’d block a mailbox from accessing a protocol like IMAP4 or Exchange ActiveSync.

Set-CasMailbox -Identity Kim.Akers -OneWinNativeOutlookEnabled $False

When the block is in place, the new client fails to connect to the user mailbox and issues the error shown in Figure 3.

The Project Monarch client is blocked from synchronizing with a mailbox
Figure 3: The Project Monarch client is blocked from synchronizing with a mailbox

Microsoft suggests that organizations use the block to prevent people from using the new client until the official beta is ready. In other words, they’d like you to run some code like this:

Get-ExoMailbox -RecipientTypeDetails UserMailbox -ResultSize Unlimited | Set-CasMailbox -OneWinNativeOutlookEnabled $False

And when Microsoft releases the official beta, you can reverse the block with:

Get-ExoMailbox -RecipientTypeDetails UserMailbox -ResultSize Unlimited | Set-CasMailbox -OneWinNativeOutlookEnabled $True

The Slow Pace of Development

After all the excitement dies down, we’re left with the conclusion that Project Monarch is moving ahead, albeit slowly. We see the tip of the iceberg in the leaked client. Underneath, I’m sure that Microsoft is working through a bunch of software engineering challenges to create the foundation for a single base that can support multiple variations of Outlook clients. We await the news of the official beta as promised by Microsoft.

So much change, all the time. It’s a challenge to stay abreast of all the updates Microsoft makes across Office 365. Subscribe to the Office 365 for IT Pros eBook to receive monthly insights into what happens, why it happens, and what new features and capabilities mean for your tenant.

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