November 2026 · Folder Suggest

Outlook Not Responding or Keeps Crashing: Safe Mode, Repair and Other Fixes

Outlook shows “Not responding,” freezes, closes by itself or takes ages to open a message. Work through the fixes below in order: the first ones are quick and change nothing you can lose.

In short: in classic Outlook for Windows, first wait a few minutes and look for a hidden dialog box (press Alt+Tab). Then start Outlook in safe mode with outlook.exe /safe (or hold Ctrl while you open it). If it works there, turn off add-ins in File > Options > Add-ins > COM Add-ins > Go. Next, install updates, run Microsoft’s Classic Outlook Advanced Diagnostics troubleshooter, repair Office (Quick Repair, then Online Repair), run the Inbox Repair Tool (SCANPST.EXE), and create a new profile. In new Outlook, end the task in Task Manager, then use Repair under Installed apps > Outlook (new) > Advanced options. Never delete a .pst file.

What You Can Try in Each Outlook

Outlook	Main fixes Microsoft documents
Classic Outlook for Windows	Wait for tasks, safe mode, COM add-ins, updates, Get Help troubleshooter, Office repair, SCANPST.EXE, new profile
New Outlook for Windows	End the task and restart, Repair or Reset in Windows Settings, reinstall from the Microsoft Store. Microsoft documents no safe mode for it, and the Get Help troubleshooter doesn’t work with it
Outlook on the web and Outlook.com	Check service status, try another browser, turn off ad blockers and extensions, clear cache and cookies
Outlook for Mac	Install updates, check Microsoft’s known issues list. Microsoft’s safe mode steps are for Windows only

Not sure which Outlook for Windows you have? See new Outlook vs. classic Outlook. The classic steps below follow Microsoft’s Outlook for Windows not responding, hangs, freezes, or stops working and its longer troubleshooting article.

Outlook Not Responding? Wait, Then Look for a Hidden Dialog Box

Check the status bar at the bottom of the window. AutoArchive, a very large attachment, or moving thousands of messages can make Outlook look frozen. Microsoft says to wait, usually two or three minutes.
Press Alt+Tab to look for a dialog box hidden behind another window. Outlook waits until you answer it. Microsoft’s example is the confirmation that appears after Dismiss All on reminders.

How to Start Outlook in Safe Mode

Safe mode starts Outlook without add-ins and without your toolbar customizations. If Outlook works in safe mode, the problem is most likely an add-in. There are two ways to start it:

With a command: close Outlook. Press the Windows logo key + R to open Run, type outlook.exe /safe, and select OK. That is the spelling in Microsoft’s not-responding article; its safe mode page writes outlook /safe.
With the Ctrl key (from the same safe mode page): find the Outlook shortcut, hold Ctrl and double-click it, then select Yes when asked whether to start in safe mode.

If a Choose Profile box appears, accept the default profile. Enter your password if asked. To leave safe mode, close Outlook and open it as usual. Stuck on the “Processing” screen? Microsoft’s Processing article says to start once in safe mode, close Outlook, then open it normally.

Outlook Keeps Crashing? Turn Off Add-ins

With Outlook open in safe mode, go to File > Options > Add-ins.
Select COM Add-ins, then Go.
Write down or screenshot which add-ins are ticked, clear all the check boxes, and select OK.
Close Outlook and open it normally.
If the problem is gone, turn the add-ins back on one at a time, restarting Outlook after each. When the problem returns, the last one you turned on is the cause. Leave it off.

Microsoft’s warning: clear the check box, don’t select an add-in and choose Remove.

Install Windows and Office Updates

Office: in classic Outlook, go to File > Office Account > Update Options > Update Now. If Update Now isn’t shown, select Enable Updates first. If there is no Update Options button, only About, your organization manages updates. Ask your help desk.
Windows: go to Settings > Windows Update and check for updates.

Microsoft’s Automated Troubleshooter: Support and Recovery Assistant Is Now Get Help

Microsoft says the Microsoft Support and Recovery Assistant has been replaced with troubleshooters in the Windows Get Help app, though some older articles still link to it. For a freezing or slow Outlook, run the Classic Outlook Advanced Diagnostics troubleshooter. Microsoft says it can check many of the causes below automatically, so it is worth running before you repair anything. If a pop-up says “This site is trying to open Get Help,” select Open, then follow the steps in Get Help.

Run it on the PC where classic Outlook is installed, on Windows 10 or later.
It doesn’t work in new Outlook.
Your organization may have turned Get Help off.

Outlook Repair: Repair Office

Close every Office app first. Following Microsoft’s Repair an Office application:

Windows 11: right-click Start, select Installed apps, find Microsoft 365 or Office, select the three dots, then Modify. Windows 10: right-click Start, select Apps and Features, select the product, then Modify.
Choose Quick Repair or Online Repair, then Repair. (On some older volume-licence installs you’ll see only Repair and Continue instead.)
Restart your PC if asked.

Quick Repair is faster and only replaces damaged files. Online Repair is more thorough, but Microsoft says it needs an active internet connection. Try Quick Repair first, and use Online Repair if that doesn’t help. Either one repairs the whole Office suite.

Repair the Outlook Data File With SCANPST.EXE

The Inbox Repair Tool scans an Outlook data file for errors and fixes them. Per Microsoft’s data file repair page:

To see where your files are, go to File > Account Settings > Account Settings and open the Data Files tab. Then exit Outlook.
Open SCANPST.EXE. For Outlook 2016 and 2019, Microsoft lists C:\Program Files (x86)\Microsoft Office\root\Office16. If it isn’t there, search for SCANPST.EXE in File Explorer.
Select Browse, pick the .pst file, and select Start.
If errors are found, select Repair. The tool keeps a backup (.bak) copy of the file in the same folder. You may need to run it more than once.

Recovered items may appear in a Lost and Found folder. The tool doesn’t look at mail stored in an Exchange or Microsoft 365 mailbox on the server.

Outlook Very Slow? Check the Size of Your Mailbox

Big folders slow Outlook down. Microsoft’s large mailbox article sets no hard limit, but says performance can drop as you approach 100,000 mail items in one folder, 10,000 folders, or 10,000 calendar items.

Move items out of your largest folders, such as the Inbox, into other folders, or archive them.
Go to File > Tools > Mailbox Cleanup to see your mailbox size, find large or old items, and empty the Deleted Items folder.
After deleting, compact the file: File > Account Settings > Account Settings > Data Files, select the file, Settings, then Compact Now. For Exchange and Outlook.com accounts, it’s under the Advanced tab, Outlook Data File Settings.

Create a New Outlook Profile

A profile holds your accounts, data files and settings. If a new one fixes the problem, the old one was damaged. Using Microsoft’s profile steps:

Hold Shift while you start Outlook, or press Windows logo key + R and run Outlook.exe /profiles.
In the profile box, select Options, then tick Prompt a profile to be used so you can switch back.
Select New, type a name, select OK, and add your email account.

What this does to your mail:

Microsoft 365, Exchange and Outlook.com accounts: Outlook keeps a synchronized copy of the server mailbox in an .ost file. The new profile downloads that copy again from the server, which can take a while for a large mailbox.
POP accounts: your mail lives only in a .pst file on your PC. Don’t delete it. If the new profile doesn’t show your old mail, open the file with File > Open & Export > Open Outlook Data File.

Keep the old profile until you are sure the new one works.

New Outlook Not Responding or Crashing

Restart it properly. Right-click Start, open Task Manager, select Microsoft Outlook, choose End task, then open Outlook again.
Repair the app. Right-click Start, open Installed apps, search for Outlook, select the three dots next to Outlook (new), then Advanced options and Repair. Microsoft’s Repair Outlook page says Repair doesn’t delete the app’s data.
Reset only if Repair fails. Reset is on the same page, and Microsoft says it deletes the app’s data.
Reinstall. Uninstall new Outlook from the Start menu and get it again from the Microsoft Store. It needs Windows 10 version 17763.0 or later.

Outlook on the Web and Outlook.com Slow or Not Loading

From Microsoft’s Outlook.com known issues page:

Check Microsoft’s service status page for an outage. With a work account, your admin can see more under Health > Service health in the Microsoft 365 admin center (Microsoft’s steps).
Try Microsoft Edge or another browser.
Turn off ad blockers and other extensions for Outlook, then refresh.
Clear your browser’s cache and cookies, then sign in again.

Outlook for Mac Freezing or Crashing

Update first. In Outlook, choose Help > Check for Updates, then Update. If you installed Outlook from the Mac App Store, update it there instead (Microsoft’s steps).
Check known issues. Microsoft keeps a list of recent issues in Outlook for Mac, including bugs that made it stop responding, with fixes and workarounds.

Frequently Asked Questions

How do I open Outlook in safe mode?
In classic Outlook for Windows, close Outlook, press Windows logo key + R, type outlook.exe /safe, and select OK. Or hold Ctrl while you double-click the Outlook shortcut and select Yes. Close and reopen Outlook to leave safe mode. Microsoft documents this for Windows only.

Why does Outlook keep crashing?
Microsoft lists add-ins, missing updates, damaged Office files, a damaged data file, a very large mailbox, antivirus conflicts and a damaged profile as common causes. If Outlook works in safe mode, an add-in is the likely cause. Turn them off under File > Options > Add-ins > COM Add-ins > Go.

Why is Outlook so slow?
Usually a large mailbox, a background task such as AutoArchive or a big attachment, or an add-in. Microsoft says performance can drop near 100,000 items in one folder or 10,000 folders. Move or archive items from your largest folders, and check the status bar for tasks still running.

Will repairing Office or using SCANPST.EXE delete my email?
Quick Repair only finds and replaces damaged program files. SCANPST.EXE keeps a backup (.bak) copy of your data file during the repair, though items damaged beyond repair may be lost. Never delete a .pst file: for a POP account, that is where your mail is stored.

Is the Microsoft Support and Recovery Assistant still available?
Microsoft says it has been replaced with troubleshooters in the Windows Get Help app. For classic Outlook that freezes or runs slowly, use the Classic Outlook Advanced Diagnostics troubleshooter. It needs Windows 10 or later and doesn’t work with new Outlook.

How do I fix new Outlook when it stops responding?
End Microsoft Outlook in Task Manager and reopen it. If that fails, go to Installed apps, Outlook (new), Advanced options and select Repair, which keeps the app’s data. Reset deletes the app’s data, so try it only after Repair. Reinstalling from the Microsoft Store is the last step.