You've probably seen the prompts already.
Microsoft is steadily moving users towards the New Outlook experience. Microsoft has confirmed that from March 2027, New Outlook will become the default for business users. You'll still be able to switch back to Classic for a while, but the clock is ticking. Many have changed already, but there are others for whom the switch comes with that prickly back-of-the-mind fear - "If we switch, what's going to break?"
The short version is that for many businesses, nothing major will break.
If Outlook is simply where you read emails, manage your calendar and book Teams meetings, the move is likely to be straightforward.
The businesses that need to pay attention are those for whom Outlook has quietly become the hub for other systems too. CRM platforms, document management systems, project management tools and compliance software often plug directly into Outlook. Some of those integrations may need updating before you make the switch. Microsoft states that New Outlook supports web add-ins, whilst older COM add-ins are not supported. It's not just add-ins either. Macros (VBA) don't work in New Outlook at all. So before you panic, let's keep it simple.
Grab a brew - let's work through this quick self-assessment together.
First things first.
Open Outlook and look towards the top-right corner.
If you see a toggle that says "Try the New Outlook" or "New Outlook" with the toggle grey rather than blue, you're almost certainly still using Classic Outlook.
If you've already switched and everything works as expected, you can probably relax.
If you're still using Classic Outlook, move on to Step 2.
Here's where things get interesting.
Think about how your team actually uses Outlook.
Do any of these sound familiar?
Save emails into a CRM
Save emails into project or customer folders
Send contracts for signature
Attach emails to support tickets
Archive emails automatically
Use buttons added by third-party software
File emails into document management systems
Use specialist legal, financial or compliance software
Run macros or automated scripts
Click-to-dial from your phone system
Open old PST archive files
If you answered "yes" to any of those, Outlook is doing more than just email. That's where compatibility checks become important.
This is one of the easiest checks.
Open Outlook and look across the ribbon (if your ribbon isn't very large you may have it minimised. Look for a down arrow in the top-right to open it up)
Do you see buttons from:
Salesforce
Smartsheet
Dynamics 365
If you do, make a list.
Every button is effectively an integration that should be checked before moving everyone to New Outlook.
A quick example: We've seen businesses assume Outlook is "just Outlook", only to discover six months later that nobody remembered the software used to file customer emails into their project system.
That's usually when things become exciting. And not in a good way.
Imagine if Outlook vanished tomorrow - what jobs couldn't people do?
It's a simple question, but it uncovers most risks.
For example:
Good news for Teams users: booking Teams meetings is built into New Outlook, so you don't need the old Teams add-in.
If an Outlook integration supports a business process, it deserves a compatibility check.
Most software suppliers have already prepared guidance for New Outlook.
Search their website for:
If the vendor has clear documentation explaining how their integration works with New Outlook, that's usually a good sign.
If support articles are several years old and only discuss desktop Outlook plugins, it's worth asking more questions.
One example is Smartsheet. Its current documentation specifically references support for New Outlook (which Microsoft also calls 'One Outlook') through its Outlook add-in.
You're probably in good shape.
A little testing before migration would be sensible.
Definitely worth doing a review before rolling New Outlook out to everyone.
It's easy to see the move as a nuisance.
In reality, Microsoft is trying to modernise the platform.
New Outlook uses a modern web add-in model rather than the older COM add-in approach. Microsoft's guidance notes that web add-ins operate in a more controlled, sandboxed environment designed to improve stability and reduce issues caused by traditional Outlook plugins.
For businesses, that can mean:
The transition may require some planning, but the direction of travel is positive.
Don't focus solely on Outlook. Focus on the things that connect to Outlook.
Most migration issues aren't caused by email. They're caused by forgotten integrations that nobody realised the business was relying on. So before Microsoft's switch catches you by surprise:
A couple of hours spent checking now is usually a lot less painful than discovering an important workflow has stopped working on a Monday morning.
If you're unsure whether your business is at risk, a straightforward Outlook readiness review can quickly identify any integrations or workflows that might need attention before the switch to New Outlook.