If Classic Outlook freezes, crashes, will not start, or stops sending and receiving, begin with the symptom: check for a blocked dialog or background task, then test Safe Mode before moving to a new profile or software repair. These steps apply to Classic Outlook for Windows—not new Outlook for Windows.
First, confirm which Outlook you use
This guide is for Classic Outlook for Windows. Microsoft’s Classic-specific instructions and the Outlook troubleshooters in Get Help do not apply to new Outlook for Windows. If you are unsure, check which Outlook app is open before following the steps below.
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Next, note the exact symptom and any message on screen. “Outlook not responding,” a freeze at “Processing,” “Cannot start Microsoft Outlook,” a message stuck in the Outbox, or a status of “Disconnected,” “Working Offline,” or “Trying to connect…” point toward different checks.
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Check for a blocked dialog or background task
- Press Alt+Tab to look for a confirmation window hidden behind Outlook. Respond to it if one is waiting.
- Check Outlook’s status bar. If it indicates background work—such as AutoArchive or processing a large attachment—give it a short time to finish before closing the app.
For a “Processing” screen, Microsoft’s documented first step is to close Outlook, start it in Safe Mode, close it again, and reopen it normally. Open the Windows Run dialog, enter outlook.exe /safe, and press Enter. If Windows cannot find the command, use the full path to Outlook.exe for your Office installation.
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Update before deeper repair
Install available Office and Windows updates. If the problem continues, follow the add-in, profile, data-file, and Office repair checks below in that order. Before applying an older workaround, compare your installed Office build and symptom with Microsoft’s current known issues for Office; reported problems and fixes can change.
If Outlook crashes or will not start
Test Safe Mode and isolate add-ins
- Close Outlook. Press Windows+R, type
outlook.exe /safe, and press Enter. If Outlook opens, an add-in is one possible cause. - In Outlook, open File > Options > Add-ins. Beside Manage, choose COM Add-ins, then select Go.
- Clear the check box for each enabled COM add-in and select OK. Disable them for diagnosis rather than removing them.
- Restart Outlook normally. If the problem is gone, return to the same COM Add-ins list, enable one add-in, and restart Outlook. Repeat one at a time until the problem returns; the last enabled add-in is the likely conflict.
If Outlook still fails in Safe Mode, add-ins are less likely to explain the problem. Continue with a new profile and repair steps.
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Test with a new Outlook profile
A new profile helps distinguish a profile problem from a broader Outlook or Office issue. Create and select a new profile using Windows’ Mail setup for Outlook profiles. The exact location can vary by Windows version; you can search Windows for Control Panel, open Mail (Microsoft Outlook), choose Show Profiles, and add a profile. Set Outlook to prompt for a profile or choose the new one, then start Outlook and test it.
If Outlook works with the new profile, Microsoft’s diagnostic guidance identifies the old profile as corrupt and the source of the problem. Keep the old profile until you have confirmed that the new one has the account and data you need.
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Repair a potentially damaged data file
If the issue may involve a damaged Outlook data file, use Microsoft’s Inbox Repair Tool, scanpst.exe, to scan and repair it. Close Outlook first. The tool’s location depends on the Office installation, so search the Office installation folders for SCANPST.EXE if it is not easy to find. Select the relevant data file and follow the tool’s prompts. Make a backup copy of the file before repair when possible.
Repair Office program files
If Outlook or Office files may be damaged, run Office repair from Windows: open Settings > Apps > Installed apps (or Apps & features on some Windows versions), select Microsoft 365 or Office, choose Modify, and run Quick Repair first. If that does not resolve the issue, run Online Repair. Online Repair is more thorough and may require signing in or reconnecting Office afterward.
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If Outlook cannot send or receive mail
Check connection and offline status
- Check Outlook’s status bar for Disconnected, Working Offline, or Trying to connect….
- Confirm that the PC has an internet connection by opening another site or app.
- In Outlook, select the Send/Receive tab and turn off Work Offline if it is enabled. Try sending or receiving again.
If connection or sign-in problems come and go, Microsoft’s Get Help app offers Classic Outlook troubleshooters for intermittent connectivity and authentication issues. On Windows 10 or later, search for Get Help and run the Outlook troubleshooter on the affected PC. The tool must run on that PC.
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Check the Outbox, account password, and mailbox storage
- Large or stuck message: Open the Outbox and look for a message with a large attachment. Provider size limits vary. Remove or reduce the attachment, or send a link to the file instead, then try again.
- Changed password: If you changed the account password on your email provider’s website, update the saved credentials Outlook uses for that account.
- Mailbox storage: Check the account’s cloud mailbox storage. A full mailbox can prevent sending or receiving.
If these checks do not fix mail flow, use the profile, Safe Mode, data-file, and Office repair steps above, choosing the one that fits your symptoms.
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How to interpret the diagnostic results
| What you observe | What it suggests | Next step |
|---|---|---|
| Outlook works in Safe Mode | An add-in may be interfering. | Disable COM add-ins, then enable and restart one at a time. |
| Outlook works with a new profile | Microsoft’s guidance identifies the old profile as corrupt and the source of the issue. | Use the new profile and confirm the account and data you need are available. |
| Outlook remains broken in Safe Mode and with a new profile | The issue may involve a data file or Office program files rather than an add-in or the old profile. | Consider Inbox Repair Tool, then Office repair. |
| Status says Disconnected, Working Offline, or Trying to connect | Outlook may not have a working connection or may be set to work offline. | Check internet access and turn off Work Offline. |
| A known-issues entry matches the symptom and installed build | A version-specific Outlook issue may be involved. | Follow Microsoft’s current guidance for that issue and build. |
Do not apply historical fixes without checking your build
Microsoft documented a specific incident beginning around March 12, 2026, in which some older Classic Outlook builds could crash and prompt users to start in Safe Mode when paired with a newer Teams Meeting Add-in. Microsoft marked that issue fixed and advised updating Office; Online Repair or temporarily disabling the Teams Meeting Add-in were alternatives for the affected configuration. This was a dated, version-dependent issue—not a general explanation for Outlook crashes. Check the current known-issues page and your installed build before using its workaround.
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