Project One Outlook – see how the new Outlook for Windows is different from its predecessor

The new Outlook for Windows has been available in preview for some time now. It’s high time to see how it came into existence and how it’s different from the classic Outlook experience.

New Outlook for Windows (One Outlook) OG

How to test the new Outlook for Windows

The Try the new Outlook toggle lets any Microsoft 365 user enable a separate (new) Outlook version. You can launch either version from the start menu. They have the same name, so the only quick way to distinguish them is to look at the icon: The new Outlook has the Pre annotation, at least for the time being:

Outlook vs New Outlook icon

New Outlook for Windows release roadmap

Here are some dates related to the Outlook Monarch project that let the new Outlook come into existence.

  1. Back at Microsoft Ignite 2020, Microsoft unveiled some of the plans for making the Outlook client more uniform.
  2. Then, the first materialization of those plans was Project Monarch – a leaked build of the popular email client. It emerged in May 2022 and shown a ‘pretty much OWA’ for desktop.
  3. September 28, 2022: First release of the new Outlook for Windows for Office Insiders.
  4. April 4, 2023: The new Outlook is available in Public Preview.
  5. After the end of 2024, Mail and Calendar Apps on Windows 11 will become Outlook (the new Outlook).

The last point is worthy of some additional comment. Mail, Calendar and People Apps are free, unlike the current Outlook for Windows. So, users without a paid Microsoft 365 subscription will have access to the new Outlook but with some ads displayed.

The project One Outlook (Outlook Monarch) makes a lot of sense – instead of providing different Outlook experience on each platform, which must take a lot of dev teams resources, the app will (eventually) get the unified looks.

So, the crucial question for now is whether try the new Outlook for Windows or not. To get a clear picture, let’s have a look at the most notable differences.

How is the new Outlook for Windows different?

It’s Outlook on the web, but on desktop. The resemblance is undeniable. Still, the looks and feeling are but a small part of the changes introduced to the new Outlook. Below are some important differences between the new Outlook and the old one:

Removed features

  • COM add-ins won’t work anymore. The new Outlook for Windows supports only web-based add-ins. It’s not necessarily a bad thing, because many COM add-ins are performance-challenged. However, there are some useful COM add-ins, so you might want to look for replacements.
  • No more relying on Outlook profiles (Control panel > Mail > Profiles). Outlook profiles let you easily switch between different settings, especially useful for demo environments. On the other hand, without Outlook profiles, there’s no need to recreate them, for example after a migration.
  • No support for OST / PST files.
  • The ’old‘ Outlook allowed you to cache chosen mailbox content locally. It worked miracles when it comes to speeding up search, discovery and opening items. The new Outlook currently doesn’t have any cached, offline or local mode.

Changed features

  • Outlook settings are moved from File > Options to Settings. That’s inherited from Outlook on the web, as well. If you’re used to the old way of setting up your Outlook, the switch might take some getting used to. Here’s a quick look at both settings windows:
classic Outlook for Windows settings
New Outlook for Windows settings
  • Signature settings are in the cloud. While this is not a shocker after Microsoft introduced signature cloud settings, it is an important change – in the new Outlook, there’s no way back to local email signatures. If you have some problems (like missing email signatures) after the switch, see how to solve them in this article.
  • In the new Outlook, you can Save emails to the EML format only. The old one supported saving emails to: MSG, TXT, HTML, OFT and MHT formats.
  • Outlook rules – some of the actions known from the old Outlook for Windows are no longer available, including: have server reply with a message, reply using a template, flag, clear flag, clear categories, play a (custom) sound, print, apply retention policy and display a desktop alert.

New features

  • Easy access to Microsoft To Do, Viva Engage (Yammer), Bookings, OneDrive and the rest of the Office suite (Word, Excel, OneNote, PowerPoint) from the side pane.
  • Pinning, snoozing and scheduling emails.
  • Loop components (elements that allow real-time collaboration directly in emails).

Here is some more information on the new Outlook:

Things to know about the new Outlook for Windows

CodeTwo vs. the new Outlook

CodeTwo Email Signatures 365 (our email branding management tool) fully supports both the legacy and the new Outlook. Our modern Web Add-in was featured on Microsoft Build as one of the best examples on how to use the possibilities offered by the new Outlook (and API related to it).

However, if you’re still using any of our freeware COM add-ins (some of them were popular back in the day!), it’s time to wave them goodbye. The new Outlook for Windows offers no way to support COM add-ins. And if you still use our legacy COM Add-in to insert signatures in Outlook (client-side/Outlook mode), it’s high time for an upgrade.

Troubleshooting – Something went wrong when launching the new Outlook for Windows

Problem description

When you launch the new Outlook for Windows, you are prompted to sign in. The sign-in attempt ends with the error message:

Something went wrong

We ran into an error – Error: GlobalSettingsAccountLogonFailed

or similar.

Outlook: Something went wrong. We ran into an error - Error: GlobalSettingsAccountLogonFailed


Go to your local AppData folder (C:\Users\YourUserName\AppData\Local\Microsoft) and delete the Olk folder. If it doesn’t help, delete the OneAuth folder, too. Try running the new Outlook for Windows again.

New Outlook for Windows troubleshooting - delete Olk folder


It took me much more time than I’d like to admit to fix this problem.

When first trying to launch the new Outlook for Windows in a lab environment, I was prompted to sign in with another user’s credentials. The problem was that the account of the user was long gone – neither the user nor their Microsoft 365 tenant existed any more. It didn’t prevent the user’s profile from being cached, though.

Unlike the standard sign-in prompt, this one didn’t let me sign in as another user. First attempt to close the sign-in window caused it to appear once again. The second one returned the LogonFailed error.

What I tried:

  • Repairing and reinstalling the Office suite (Microsoft 365 Apps for Business).
  • Clearing all the info in the Windows Credential Manager.
  • Deleting & recreating all Outlook profiles.

None of these actions made any impact. The search for the cached profile location was the final step before dropping the ’format c‘ bomb on my lab environment.

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