New Outlook vs classic Outlook on Windows

For two decades, "Outlook for Windows" meant the classic Win32 application built on a long lineage. In 2024, Microsoft began rolling out the new Outlook for Windows, a web-based client that shares its codebase with Outlook on the web (OWA) and the new Outlook for Mac. Knowing what's the same and what's not avoids unhappy surprises — this is one of the few Microsoft 365 changes that every single user sees, so it deserves more planning than most feature rollouts get.

What the new Outlook is

The new Outlook is the OWA codebase running inside a desktop wrapper. It looks, feels, and updates like the web client — same UI conventions, and features ship to both at the same time. It connects to Exchange Online via modern sync and Microsoft Graph APIs rather than the older MAPI/RPC channel, which is precisely why the classic client's deepest extension points (COM, VBA, MAPI-based tools) don't carry over.

Understand what this means architecturally: Microsoft now maintains one Outlook codebase for web, Windows, and Mac instead of three. That's why the new client gets features first and why the classic client's roadmap is maintenance-only. The direction is not in doubt; only the timeline is.

What the new Outlook is good at

• Faster feature rollout — new features arrive on the new client first, and some (newer Copilot capabilities, themes, some scheduling features) never reach classic at all.
• Better integration with Microsoft 365 Copilot, Loop, and Teams.
• Modern account handling — multiple work and personal accounts, including Gmail and iCloud, in a single app.
• Lighter resource use for typical mailbox sizes, and none of classic Outlook's OST corruption or profile-rebuild rituals.
• Familiar OWA experience for users who already lived there.

What it doesn't do (still true in 2026)

The new Outlook has reached feature parity with classic for most mainstream use, but the remaining gaps are structural, not backlog items:

• COM add-ins will never be supported. The new client supports web add-ins via Office.js only. Vendors of classic-only add-ins (CRM connectors, dictation tools, records-management plugins) either ship a web add-in or their integration dies with classic.
• VBA and macros — classic only, permanently.
• PST files — support has been arriving in stages (opening and viewing came before full import/export workflows); if your organisation still leans on PSTs for archiving, treat the migration as the trigger to finally move that data into Exchange Online archiving instead.
• Offline support is functional (mail, calendar, contacts with a rolling window) but not equivalent to a full local OST replica — heavy travellers notice.
• Deep MAPI integrations — line-of-business apps that programmatically drive classic Outlook (mail-merge tools, some ERP mail flows) need re-engineering.

For users with deep classic-Outlook customisations, the gap remains material. For everyone else, it has mostly closed.

How Microsoft is rolling it out

The new Outlook is the default for new Microsoft 365 users, and Microsoft has been migrating existing users in waves — starting with smaller business SKUs, with enterprise SKUs on a slower, policy-controllable schedule. Existing users see the "Try the new Outlook" toggle. Classic Outlook remains supported into the 2029 timeframe under Microsoft's published lifecycle, so this is a managed multi-year transition, not a cliff — but new investment stopped some time ago.

IT controls the pace with the NewOutlookMigrationUserSetting and admin-controlled migration policies, Intune settings-catalog policies to hide or pin either client, and the Office Deployment Tool to include or exclude the new client in installs. Use them: an uncontrolled toggle rollout is how you end up supporting both clients indefinitely with no plan.

What admins should do

1. Inventory classic-only dependencies first — COM add-ins, VBA workflows, PST usage, MAPI-driven line-of-business apps, and shared-mailbox edge cases. This inventory is the project plan; everything else is scheduling.
2. Pressure add-in vendors now for web add-in versions, or budget replacements. This is the long-pole item in almost every migration.
3. Pilot with a mixed group — not just IT. Include an executive assistant managing delegate calendars and shared mailboxes; that persona hits more edge cases than anyone.
4. Control the toggle by policy rather than letting users drift between clients — support tickets double when nobody knows which Outlook the caller is looking at.
5. Communicate the UI change — the new client is different enough (simplified ribbon, settings in different places, no classic profile model) that a short "what moved where" guide pays for itself immediately.

For most users in 2026, the new Outlook is the right default, and fighting the direction is wasted effort — the useful work is sequencing your dependencies so the switch is boring. Just don't migrate everyone on the same day.