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Microsoft Outlook can fail to open or crash unexpectedly due to a corrupt profile, damaged data files, a misbehaving add-in, or a bloated cache. Work through the sections below in order — most issues are resolved before you reach the later steps. If a step resolves your problem, you do not need to continue further.
Before you begin, ensure your operating system and Microsoft 365 / Office installation are fully up to date. Pending Windows or Office updates are a common cause of instability.

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1. Start Outlook in Safe Mode

Safe mode launches Outlook without add-ins or customizations, which quickly isolates whether a third-party extension is causing the crash.
1

Open the Run dialog

Press Win + R to open the Run dialog box.
2

Launch Outlook in Safe Mode

Type the following command and press Enter:
3

Observe the result

If Outlook opens successfully in safe mode, an add-in is almost certainly the cause. Proceed to disable add-ins in the next section. If Outlook still crashes in safe mode, skip ahead to Profile Repair.

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Disable Add-ins

1

Open the Add-ins Manager

In Outlook, go to File → Options → Add-ins.
2

Manage COM Add-ins

At the bottom of the screen, ensure COM Add-ins is selected in the Manage drop-down, then click Go.
3

Disable all add-ins

Uncheck every listed add-in and click OK.
4

Restart Outlook normally

Close Outlook and reopen it without the /safe flag. If it loads correctly, re-enable add-ins one at a time — restarting each time — until the offending add-in is identified.
Common problem add-ins include antivirus integrations (e.g., Norton, McAfee), Adobe Acrobat PDF Maker, and Skype for Business. Disable these first to save time.

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2. Repair the Outlook Profile

A corrupt mail profile can prevent Outlook from loading entirely, even in safe mode.
1

Open Mail settings

Close Outlook. Open Control Panel → Mail (Microsoft Outlook) — you can also search for “Mail” in the Start menu.
2

Open Profile Management

Click Show Profiles.
3

Create a new profile

Click Add, give the profile a name (e.g., OutlookNew), and follow the account setup wizard to reconnect your email account.
4

Set the new profile as default

Under When starting Microsoft Outlook, use this profile, select Always use this profile and choose your new profile from the drop-down.
5

Restart Outlook

Open Outlook normally. If it launches successfully, your original profile was corrupt. You may delete the old profile from the Show Profiles screen after confirming your data is intact.
Do not delete your old profile until you have verified that all your emails, contacts, and calendar items are accessible in the new profile. Deleting the profile removes its associated configuration but does not delete your OST/PST data files on disk.

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3. Repair OST / PST Data Files with ScanPST

Outlook stores your mailbox data locally in an OST (online) or PST (archive/POP3) file. Corruption in these files causes crashes, missing emails, and send/receive errors.
1

Close Outlook completely

Ensure Outlook is fully closed before running the repair tool. Check Task Manager (Ctrl + Shift + Esc) and end any OUTLOOK.EXE processes if needed.
2

Locate ScanPST.exe

The Inbox Repair Tool is installed with Office. Common locations:
If you cannot locate it, open File Explorer and search your C:\ drive for SCANPST.EXE.
3

Locate your data file

Your OST or PST file is typically found here:
You can also find the exact path in File → Account Settings → Account Settings → Data Files tab.
4

Run the repair

Open SCANPST.EXE, click Browse, navigate to your data file, and click Start. The scan may take several minutes for large mailboxes.
5

Repair errors

If errors are detected, ensure Make a backup of scanned file before repairing is checked, then click Repair.
6

Reopen Outlook

Once repair completes, open Outlook and verify the issue is resolved. You may need to run ScanPST multiple times for severely corrupted files.
ScanPST repairs file structure issues but cannot recover permanently deleted items. For severe OST corruption, it is often faster to delete the OST file entirely — Outlook will re-download your mailbox from the server on next launch (Exchange/Microsoft 365 accounts only).

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4. Clear the Outlook Cache

A corrupted or oversized local cache can cause slowness, search failures, and crashes.
1

Close Outlook

Ensure Outlook is fully closed.
2

Open the RoamCache folder

Press Win + R, paste the following path, and press Enter:
3

Delete cache files

Select all files in this folder (Ctrl + A) and delete them. These files are automatically regenerated the next time Outlook launches.
4

Restart Outlook

Open Outlook and allow it to rebuild the cache. Initial load may be slightly slower than usual.

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5. Rebuild the Autocomplete Cache

If Outlook suggests incorrect or outdated email addresses when composing messages, the autocomplete (nickname) cache may be corrupt.
1

Open the Outlook NK2 / autocomplete cache location

Press Win + R and enter:
2

Delete the RoamCache autocomplete file

Look for a file named RoamCache\Stream_Autocomplete_*.dat. Delete this file.Alternatively, you can clear autocomplete from within Outlook: go to File → Options → Mail, scroll to the Send Messages section, and click Empty Auto-Complete List.
3

Restart Outlook

Outlook will build a fresh autocomplete cache as you send new messages.
If you need to preserve known-good autocomplete entries before clearing, export the cache using the free NK2Edit utility before deleting it.

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6. Recreate the Mail Profile (Full Reset)

If earlier steps have not resolved the issue, performing a complete profile recreation from scratch is the most thorough client-side fix.
1

Back up your PST files

Copy any local PST files (typically in Documents\Outlook Files) to a safe location before proceeding.
2

Remove the existing profile

Open Control Panel → Mail → Show Profiles, select your current profile, and click Remove.
3

Delete residual cache and config files

Press Win + R and open:
Delete all files in this folder (your email data on the server is unaffected for Exchange/Microsoft 365 accounts).
4

Create a fresh profile

Return to Control Panel → Mail → Show Profiles → Add, and configure your account from scratch using your email address and credentials.
5

Launch Outlook

Open Outlook with the new profile and allow it to complete the initial mailbox synchronization.

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Escalation

Escalate if any of the following apply after completing all steps above:
  • Outlook continues to crash in safe mode with all add-ins disabled.
  • ScanPST reports it cannot repair the data file.
  • You receive activation errors (e.g., “Product Deactivated” or licensing prompts).
  • The issue affects multiple users simultaneously — this may indicate a server-side or network problem.
  • Your mailbox fails to synchronize after profile recreation, suggesting an Exchange/Microsoft 365 account provisioning issue.
When logging a ticket, include:
  • The exact error message or crash behavior observed.
  • Your Office version (File → Office Account → About Outlook).
  • Whether the issue occurs in safe mode.
  • The output of ScanPST (repaired / errors found / no errors).