New Outlook Migration Guide (2026)

Why This Guide Matters for Your Helpdesk

Microsoft is replacing classic Outlook for Windows with the "new Outlook" — a web-based client rebuilt from scratch on the same engine that powers Outlook on the Web. And if you're an IT helpdesk professional, you've probably already felt the ripple effects.

In March 2026, Microsoft pushed the enterprise opt-out deadline back to March 2027, essentially admitting that the migration wasn't going smoothly. Add-in compatibility gaps, PST file headaches, and missing features were all cited. Classic Outlook stays supported through at least 2029, but make no mistake — the transition is coming whether we like it or not.

For helpdesk teams, this means one thing: more tickets. Users losing access to PST files, COM add-ins breaking overnight, shared mailbox calendar confusion, and a completely new UI that nobody asked for training on. This guide walks through every angle — from locking down the rollout with GPO, Intune, and PowerShell to fixing the most common issues landing in your queue right now.

Understanding the Migration Timeline

Microsoft has structured the transition in three phases:

Opt-in (Current for Enterprise) — Users can voluntarily toggle into the new Outlook experience. Nothing is forced.
Opt-out (Postponed to March 2027 for Enterprise) — New Outlook becomes the default, but users and admins can still switch back to classic Outlook.
Cutover (Date TBD) — Classic Outlook gets removed entirely. No going back.

Small and medium business users on Microsoft 365 Business Standard and Premium licenses started the opt-out phase back in January 2025. Enterprise license holders now have until March 2027 before opt-out kicks in. If you're running perpetual licenses (Office 2021, 2024), classic Outlook sticks around until at least 2029.

What Triggered the Delay?

Microsoft said they wanted to "ensure organizations have the time they need to prepare." Honestly, their own feature comparison documentation tells the real story — it lists significant gaps: partial PST support, no COM add-in compatibility, limited offline mode, and missing power-user features like advanced search folders and local file path hyperlinks. The enterprise feedback was pretty clear: the new client wasn't ready for forced adoption.

Controlling the New Outlook Rollout

Before users start flipping the toggle on their own (and trust me, they will), you'll want to lock it down. Here are four methods, from enterprise-scale to quick one-off fixes.

Method 1: Group Policy (GPO)

For domain-joined Windows devices, Group Policy is still the most reliable way to hide the "Try the new Outlook" toggle from classic Outlook.

Download and import the latest Office ADMX templates from Microsoft (required if the setting isn't already available in your environment).
Open the Group Policy Management Console and navigate to User Configuration > Administrative Templates > Microsoft Outlook 2016 > Outlook Options > Other.
Enable the policy "Hide the 'Try the new Outlook' toggle in Outlook".
Link the GPO to the target OU.

Minimum version requirements:

Current Channel: Version 2304 (Build 16327.20214) or later
Monthly Enterprise Channel: Version 2303 (Build 16227.20318) or later
Semi-Annual Enterprise Channel: Build 16731.20504 or later

Method 2: Microsoft Intune

For Entra ID-joined or hybrid-joined devices managed through Intune:

Sign in to the Intune admin center and go to Devices > Windows > Configuration.
Create a new policy using the Settings Catalog profile type.
Search for "Outlook" and pick the category Microsoft Outlook 2016\Outlook Options\Other.
Enable "Hide the 'Try the new Outlook' toggle in Outlook (User)".
Assign the profile to your target device or user groups.

One thing to watch for: if you have hybrid-joined devices, make sure Group Policy settings are syncing correctly through your on-premises domain controller and that Intune is running in co-management mode. This trips people up more often than you'd think.

Method 3: Exchange Online PowerShell

You can block access to work or school mailboxes in the new Outlook at the mailbox or policy level:

# Block new Outlook for a specific user
Set-CASMailbox -Identity "[email protected]" -OneWinNativeOutlookEnabled $false

# Block new Outlook organization-wide using a mailbox policy
Set-OwaMailboxPolicy -Identity "OwaMailboxPolicy-Default" -OneWinNativeOutlookEnabled $false

# Block the built-in Windows Mail and Calendar app as well
Set-CASMailbox -Identity "[email protected]" -UniversalOutlookEnabled $false

Use Set-OwaMailboxPolicy for a policy-based approach that covers both existing and future mailboxes. Use Set-CASMailbox when you need granular per-user control.

Method 4: Registry Key (Quick Fix)

For one-off machines or testing — sometimes you just need something fast:

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Options\General]
"HideNewOutlookToggle"=dword:00000001

Set the value to 1 to hide the toggle, 0 to show it. You'll need to restart Outlook after making the change.

Removing New Outlook Entirely

If you need to fully remove the new Outlook app from devices (not just hide the toggle), here's how:

# Remove for all users on the device
Remove-AppxPackage -AllUsers -Package (Get-AppxPackage Microsoft.OutlookForWindows).PackageFullName

# Prevent reinstallation via Windows Update
Remove-AppxProvisionedPackage -Online -PackageName (Get-AppxProvisionedPackage -Online | Where-Object {$_.PackageName -like "*OutlookForWindows*"}).PackageName

To verify it's actually gone, check whether the logs folder exists at %localappdata%\Microsoft\Olk\logs. No folder? You're good.

Key Feature Gaps: What Users Will Notice

When the helpdesk tickets start rolling in, most of them will trace back to these missing or changed features. Bookmark this section — you'll be referencing it a lot.

PST File Support

New Outlook can import PST files, but only email data comes through. Contacts and calendar entries inside PST files? Not supported.
Unlike classic Outlook where PST folders appear instantly as a local folder tree, new Outlook has to upload everything to the server. For large PST files, this can take hours depending on file size and internet speed.
Full PST-to-mailbox import is on Microsoft's roadmap, expected to start rolling out in April 2026.
Before migration, run the Inbox Repair Tool (Scanpst.exe) on any PST files. Corrupted PSTs during import are not fun to troubleshoot.

COM and VSTO Add-ins

This is the big one. COM and VSTO add-ins are flat-out not supported in new Outlook. Only web-based add-ins (Office.js) work.

When a user switches to new Outlook, the web add-in counterpart of their existing COM add-ins gets installed automatically — assuming one exists.
Users blocked from installing add-ins by admin policy can't complete this migration. Make sure the My Custom Apps and My Marketplace Apps end-user roles are assigned in the Exchange Online role assignment policy.
Contact your ISVs early to ask about Office.js ports of critical add-ins. In my experience, a surprising number of third-party vendors still haven't released web-based equivalents.

Offline Functionality

New Outlook's offline capability is pretty limited compared to classic. If you have users who work in spotty connectivity environments — field staff, frequent travelers — they should stay on classic Outlook for now. Full stop.

UI and Workflow Changes

Right-click context menus are significantly trimmed down.
Information density is lower — power users who loved compact views won't find as many customization options.
Advanced search folders, Quick Parts, and mail merge? Missing or limited.
Local file path hyperlinks (e.g., \\server\share\file.docx) don't work at all.

Shared Mailbox and Calendar Delegation Issues

If I had to bet on what generates the most tickets during this migration, shared mailbox and calendar delegation would be it. Here's what you'll run into.

Shared Calendars Not Visible

Shared and delegate calendars are not visible by default in the new Outlook. Users have to navigate to "People's Calendars" and manually select which calendar they want to see. Use Split View to display multiple calendars side by side.

This catches almost everyone off guard, so consider including it in any pre-migration communication you send out.

Delegate Restrictions

Delegates can only be assigned to the primary calendar (the one named "Calendar"). Additional user-created calendars only support Editor access.
You can't grant editor or delegate access to people outside your organization.
Delegate access requires a work or school account in Microsoft 365 with Exchange Online.

Secondary Calendar Sharing Bug

Here's a frustrating one: when a user creates a secondary calendar and shares it, the recipient often can't find or add it in new Outlook. The workaround is to re-grant access via PowerShell:

# Re-grant access to the secondary calendar via PowerShell
Add-MailboxFolderPermission -Identity "[email protected]:\Calendar\Project Calendar" -User "[email protected]" -AccessRights Editor

After that, have the recipient clear their local Outlook cache and restart. The calendar should then show up under "Shared Calendars."

Full Mailbox Access vs. Calendar Delegation

This confuses people constantly: granting Full Access to a shared mailbox does not automatically share the calendar with the delegate. Calendar permissions have to be configured separately. It's been this way for years, but the new Outlook migration surfaces it again because people are re-setting up their delegations from scratch.

Known Bugs and Active Issues (March 2026)

Keeping track of these will help you get ahead of tickets before they pile up.

New Outlook — Under Investigation

Reply All broken in Microsoft 365 Groups — Users can't use Reply All in email messages within M365 groups. No workaround yet.
Print error with Word attachments — Trying to print a Word document attached to an email throws an error.

New Outlook — Workarounds Available

Email send delay — Users notice a lag when sending emails. Microsoft is aware and looking into it.
"Welcome to Outlook 2016" wizard pops up unexpectedly — Some users see the classic setup wizard after switching to new Outlook, which is confusing to say the least.

Classic Outlook — Critical Fix (January 2026 Update)

The January 13, 2026 Windows update (KB5074109) caused classic Outlook to hang or refuse to reopen, especially for users with POP accounts or PST files stored in OneDrive. Symptoms included:

Outlook showing "Not Responding"
Outlook stuck running in the background after closing
Sent items not appearing in the Sent folder

Microsoft fixed this in KB5078127. If you can't apply the fix right away, uninstalling KB5074109 works as a temporary workaround.

Security Advisory: CVE-2026-21511

This one's important. A spoofing vulnerability in Microsoft Outlook lets an attacker craft a specially designed email that triggers an outbound NTLM authentication attempt to an attacker-controlled server — potentially exposing credentials. The Preview Pane is an attack vector. Make sure your Outlook installations are patched to the latest security update as soon as possible.

Building Your Migration Playbook

A structured rollout is the difference between a manageable migration and helpdesk chaos. Here's a four-phase playbook that's worked well in practice.

Phase 1: Audit and Assess

Inventory COM add-ins across your organization. Figure out which ones have web-based equivalents and which are migration blockers.
Identify PST dependencies. Survey users who rely on local PST archives. Plan for server-side import or migration to Exchange Online Archive mailboxes.
Catalog shared mailboxes and delegation setups. Document which teams depend on shared calendars, delegation, or secondary calendar sharing.
Review Group Policy and Intune configurations. Make sure you can control the toggle before users discover it on their own (because they will).

Phase 2: Pilot

Select representative pilot groups that cover your key workflows: compose, calendar, delegation, shared mailboxes, offline use, and third-party integrations.
Hide the toggle for all users except the pilot group using GPO or Intune.
Run the pilot for at least 30 days. Track ticket volume, feature gap reports, and how users are actually feeling about the change.
Document workarounds for every single issue the pilot group runs into. Your future self will thank you.

Phase 3: Staged Rollout

Enable the toggle for departments with the fewest add-in dependencies and simplest workflows first.
Provide targeted training materials. Focus on the three biggest changes: the new navigation layout, finding shared calendars, and PST limitations.
Publish a known-issues board internally and update it weekly as Microsoft ships fixes.
Keep classic Outlook accessible as a fallback. Don't remove it from devices during the rollout period — you will regret it.

Phase 4: Monitor and Optimize

Track helpdesk ticket categories related to the new Outlook. I'd recommend creating these categories: "New Outlook — Add-in Issue," "New Outlook — Calendar/Delegation," "New Outlook — PST/Archive," "New Outlook — UI/Navigation."
Check Microsoft's official known issues page weekly for status updates.
Schedule a quarterly review of your migration timeline against Microsoft's roadmap. Things change frequently.

Essential PowerShell Commands for Helpdesk

Keep these commands bookmarked — you'll reach for them regularly during escalations:

# Check if a user has new Outlook access enabled
Get-CASMailbox -Identity "[email protected]" | Select-Object OneWinNativeOutlookEnabled

# Check the organization-wide OWA mailbox policy
Get-OwaMailboxPolicy | Select-Object Name, OneWinNativeOutlookEnabled

# Grant Full Access to a shared mailbox
Add-MailboxPermission -Identity "[email protected]" -User "[email protected]" -AccessRights FullAccess -InheritanceType All

# Grant Send As permission
Add-RecipientPermission -Identity "[email protected]" -Trustee "[email protected]" -AccessRights SendAs -Confirm:$false

# Grant calendar-specific delegate permissions
Add-MailboxFolderPermission -Identity "[email protected]:\Calendar" -User "[email protected]" -AccessRights Editor -SharingPermissionFlags Delegate

# Re-run the new Outlook migration wizard for a user
# In new Outlook: Settings > Accounts > Your Accounts > Manage > Get Started

# Repair a PST file before migration (run locally)
# Navigate to the Outlook installation directory and run:
# scanpst.exe "C:\Users\username\Documents\Outlook Files\archive.pst"

Troubleshooting Flowchart: Common Helpdesk Scenarios

User Says: "My Add-in Disappeared"

First, confirm whether they switched to new Outlook (check the toggle in the top-right corner).
If yes, check if the add-in has a web-based equivalent on the Microsoft AppSource marketplace.
If a web equivalent exists, install it through Settings > Mail > Compose and Reply > Add-ins (or deploy it centrally from the admin center).
If no equivalent exists, switch the user back to classic Outlook and hide the toggle via GPO or Intune.
Log the add-in as a migration blocker in your tracking system. This data is gold for planning.

User Says: "I Can't See My PST Folders"

Confirm whether they're on new Outlook.
Explain that new Outlook requires PST data to be uploaded to the server. Navigate to File > Open > Import to kick off the import.
Set expectations: only email data gets imported. Contacts and calendar items in the PST aren't supported yet.
For large PST files (over 2 GB), recommend running the import during off-hours. The upload can be slow and it'll eat bandwidth.
If the user needs full PST access right now, switch them back to classic Outlook.

User Says: "I Can't See the Shared Calendar"

Navigate to the Calendar view in new Outlook.
Look for "People's Calendars" in the left panel and select the shared calendar.
If the calendar isn't listed, verify permissions via PowerShell: Get-MailboxFolderPermission -Identity "[email protected]:\Calendar"
If permissions look correct but the calendar still won't show, remove and re-add the permissions.
Clear the local Outlook cache and restart. That usually does the trick.

Frequently Asked Questions

When will Microsoft force everyone to use new Outlook?

The enterprise opt-out phase has been pushed to March 2027. During opt-out, new Outlook is the default but users can switch back. The cutover phase (where there's no going back) has no confirmed date yet. Classic Outlook under perpetual licenses stays supported until at least 2029.

Can I still use COM add-ins in new Outlook?

No. COM and VSTO add-ins don't work in new Outlook — period. Only web-based add-ins built on Office.js are supported. Check with your add-in vendors for web-based alternatives, and test them thoroughly before migrating affected users.

How do I import PST files into new Outlook?

New Outlook can import email data from PST files, but contacts and calendar entries won't come through. The import uploads data to the server, so it can take a while for large files. Run Scanpst.exe on the PST first to check for corruption. Full PST-to-mailbox import is expected to start rolling out in April 2026.

Why did Outlook stop working after the January 2026 Windows update?

The January 13, 2026 update (KB5074109) caused classic Outlook to hang for users with POP accounts or PST files in OneDrive. Microsoft released fix KB5078127. If you can't install it right away, uninstalling KB5074109 works as a temporary workaround.

How do I prevent users from switching to new Outlook on their own?

Use Group Policy, Intune, Exchange Online PowerShell, or a registry key to hide the "Try the new Outlook" toggle. GPO and Intune are the recommended approaches for enterprise environments since they scale across all managed devices. Check the "Controlling the New Outlook Rollout" section above for the step-by-step walkthrough.