Microsoft Outlook

ApplicationMicrosoft Corporation

Also called outlook, classic outlook, outlook.exe

Microsoft CorporationProductivity

Classic desktop mail and calendar from Office and Microsoft 365. The process is OUTLOOK.EXE. New Outlook is olk.exe. Windows Mail is HxOutlook.exe.

What you need to know

Classic Outlook is OUTLOOK.EXE. New Outlook and Windows Mail are other clients.

This article is the Win32 Outlook that stores profiles, OST/PST files, and COM add-ins. Microsoft 365 is the suite that often installs it. The New Outlook toggle starts a different executable.

What is it?: Classic desktop Outlook
Same as New Outlook?: No. That client is olk.exe
Same as Windows Mail?: No. Mail is HxOutlook.exe

Feex says

If mail "moved" after a Windows 11 prompt, I would check whether you are still on OUTLOOK.EXE or already on olk.exe. Those are not the same client, and Windows Mail is a third one.

What is Microsoft Outlook?

Classic Microsoft Outlook is the desktop mail and calendar app whose image name is OUTLOOK.EXE. It is part of Microsoft 365 Apps or older Office. It is not New Outlook (olk.exe) and it is not Windows Mail (HxOutlook.exe).

If you have never used it

If your work mailbox has lived in Outlook for years, this is usually the classic desktop client: ribbon, profiles, and an OST cache. It is not the Microsoft 365 suite page, not the New Outlook Store app, and not the Windows 10 Mail tile. Install it with Office or Microsoft 365. The "Try the new Outlook" switch leaves this exe and starts olk.exe.

What is it used for?

Mail and calendar

Exchange, Microsoft 365, and many IMAP accounts in one Win32 window.

OST, PST, and profiles

Offline cache and personal folders. New Outlook does not treat PST the same way.

COM add-ins

Classic Outlook loads COM and VBA add-ins. olk.exe does not host that model.

Who is it for?

Work PCs that still require classic Outlook add-ins
People with PST archives they must keep opening
Anyone Windows 11 is nudging toward New Outlook

Current status

Actively developed, with Microsoft steering many consumers toward New Outlook. Classic Outlook remains the Win32 client in Microsoft 365 Apps.

How old is it?

Outlook 97 launched in 1997 and replaced Exchange Client and Schedule+ for many offices. It is not Windows Messaging from Windows 95, and it is not the 2022 New Outlook package.

Versions

Major channels first. Exact build numbers are not all verified here.

Classic Outlook (OUTLOOK.EXE)

New Outlook (olk.exe)

Outlook on the web

System requirements

Values follow the publisher's public guidance. Workload still changes the real need.

Minimum

Minimum system requirements
CPU	1.6 GHz or faster, 2-core, per Microsoft for Microsoft 365 Apps
RAM	4 GB for 64-bit, per Microsoft. A large mailbox cache wants more
Operating system	A current Windows release Microsoft lists for Microsoft 365 Apps
Other	Some Outlook features need Microsoft Edge WebView2, per Microsoft

Resource profile

CPU demand: Indexing, add-ins, and a huge inbox
RAM demand: Can stay large after a workday of mail
Disk demand: OST growth under AppData
Network demand: Exchange / Microsoft 365 sync

Installed processes

These executables belong to this product when it is installed.

Installed processes
OUTLOOK.EXE	Classic desktop Outlook

Startup components

Classic Outlook can start with Windows from its own option or a shortcut. That is not New Outlook and not the Mail app.

File locations

Common Microsoft Outlook locations
Typical Click-to-Run	C:\Program Files\Microsoft Office\root\Office16\OUTLOOK.EXE
OST / PST	C:\Users\<you>\AppData\Local\Microsoft\Outlook\

File formats

MSGPSTOSTICSEML

Common problems

The New Outlook toggle hides this client

Turn off "Try the new Outlook" if you still need PST or COM add-ins. olk.exe is a different app.

Add-ins make Outlook Not Responding

outlook.exe /safe is the classic add-in test. It does not start New Outlook.

Getting unstuck

See which Outlook you launched

Open file location. Office16\OUTLOOK.EXE is this article. olk.exe is New Outlook. HxOutlook.exe is Windows Mail.

Start classic Outlook in Safe Mode

outlook.exe /safe skips COM add-ins. scanpst.exe is the inbox repair tool for this client, not for olk.exe.

Repair Microsoft 365 Apps if classic Outlook is missing

Do not download outlook.exe from a phishing zip. Work mail wants the tenant admin if activation fails.

Alternatives

New Outlook, Outlook on the web, Thunderbird, and Windows Mail overlap for reading mail. They do not keep the same PST and COM add-in story.

Official help and downloads

Start with the vendor. Random exe sites are not a support channel.

Official contacts
Product page	www.microsoft.com/microsoft-365/outlook What Microsoft ships as Outlook
Outlook help	support.microsoft.com/outlook Profiles, sync, and crash help
Classic vs new features	support.microsoft.com/office/feature-comparison-between-new-outlook-and-classic-outlook-de453583-1e76-48bf-975a-2e9cd2ee16dd What you lose if you switch
Command-line switches	support.microsoft.com/office/command-line-switches-for-microsoft-office-products-079164cd-4ef5-4178-b235-441737deb3a6 outlook.exe versus olk.exe
Requirements hub	www.microsoft.com/microsoft-365/microsoft-365-and-office-resources CPU, RAM, and OS Microsoft lists

Related hardware

A large OST wants an SSD and enough RAM to keep classic Outlook from paging. A GPU does not speed inbox sync.

Technical details

Classic Outlook builds follow the Microsoft 365 channel. This article does not pin a build.

Sources and verification

Reviewed by Feex editorial. Last verified August 2026 Status: Feex Reviewed. How we research.

Microsoft Outlook product page · Official Outlook product
Microsoft Support: Outlook · Profiles, add-ins, and OST help
Feature comparison: new vs classic Outlook · What each client can do
Foxhole process map · First-party samples on Windows PCs. Not a lab benchmark.

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