OUTLOOK.EXE

Application ProcessMicrosoft Corporation

Also called outlook, classic outlook, outlook.exe

WindowsApplication

Classic Outlook for Windows in Microsoft 365. The newer Outlook app uses a different executable, often olk.exe, not this file.

What you need to know

This is classic Outlook. The new Outlook app is not this process.

OUTLOOK.EXE is the Win32 Outlook client that uses OST files and COM add-ins. Microsoft's newer Outlook is a separate app. SearchIndexer can also crawl Outlook mail, which is a different process.

Safe?: Yes, from Office / Microsoft 365
New Outlook?: Different exe, often olk.exe
High CPU?: A huge OST or a broken add-in

Feex says

If OUTLOOK.EXE is busy and the OST is 40 GB, I would look at add-ins and sync before I disable Windows Search. Those are different machines in the same PC.

What is OUTLOOK.EXE?

OUTLOOK.EXE is classic Outlook. It is part of Microsoft 365 Apps or older Office. It is not the Windows Mail app and it is not the new Outlook package.

What does it do?

It syncs Exchange or IMAP into an OST or PST, runs add-ins, and can keep a MAPI session alive after you close the window if another app holds Outlook.

Why is it running?

You opened mail, or an add-in or a third-party MAPI client started Outlook. A copy from a phishing attachment named outlook.exe is not Office.

Is it safe?

Usually safe

A Microsoft-signed OUTLOOK.EXE under Microsoft Office\root\Office16 is the client. The new Outlook uses another image name.

A legitimate copy normally runs from:

C:\Program Files\Microsoft Office\root\Office16\OUTLOOK.EXE

Click-to-Run Office16 path is common
New Outlook is a different app
Add-ins load in-process

Can I end it?

Closes mail and can drop unsaved items

Ending OUTLOOK.EXE kills the MAPI session. Other Office apps can stay open. Use it if Outlook is Not Responding after you saved.

Can I remove it?

Uninstall Microsoft 365 Apps

Do not delete OUTLOOK.EXE. Use Office uninstall or change the new Outlook toggle in Settings if you meant the other app.

Should it start with Windows?

Outlook can start with Windows if you left it in Startup or if a mail send from another app launches it.

Normal resource behavior

These are contextual labels, not universal averages.

CPU: Sync, rules, and a broken add-in
Memory: Grows with a large mailbox cache
Disk: OST writes
Network: Exchange / Microsoft 365

File information

OUTLOOK.EXE file information
Executable name	OUTLOOK.EXE
Common legitimate path	C:\Program Files\Microsoft Office\root\Office16\OUTLOOK.EXE
Publisher	Microsoft Corporation
Signature expectation	Signed by Microsoft Windows

Common problems

Safe mode versus add-ins

outlook.exe /safe is the documented add-in test. That does not apply to firefox.exe.

Indexer overlap

Windows Search can crawl Outlook. High disk may be SearchIndexer, not OUTLOOK.EXE. Check both rows.

Troubleshooting

Diagnose before you change anything destructive.

Disable COM add-ins from Outlook Options

One vendor add-in is a common hang. Safe mode confirms it.

Do not delete the OST as a first step

Outlook will rebuild it and the network will hurt. Repair the profile after you know it is corrupt.

Technical details

OUTLOOK.EXE technical details
Image name	OUTLOOK.EXE
Family	Microsoft 365 Apps

Sources and verification

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

Microsoft Support: Outlook system requirements · Microsoft 365 apps
Microsoft Support: Outlook not responding · Add-ins and OST
Foxhole process map · First-party samples on Windows PCs. Not a lab benchmark.

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