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> Use this file to discover all available pages before exploring further.

# Troubleshooting Outlook Not Opening, Crashing, or Slow

> Resolve Outlook crashes, profile corruption, and OST/PST file errors with these step-by-step diagnostic and repair procedures for Windows.

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.

<Note>
  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.
</Note>

## 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.

<Steps>
  <Step title="Open the Run dialog">
    Press **Win + R** to open the Run dialog box.
  </Step>

  <Step title="Launch Outlook in Safe Mode">
    Type the following command and press **Enter**:

    ```text theme={null}
    outlook /safe
    ```
  </Step>

  <Step title="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**.
  </Step>
</Steps>

### Disable Add-ins

<Steps>
  <Step title="Open the Add-ins Manager">
    In Outlook, go to **File → Options → Add-ins**.
  </Step>

  <Step title="Manage COM Add-ins">
    At the bottom of the screen, ensure **COM Add-ins** is selected in the **Manage** drop-down, then click **Go**.
  </Step>

  <Step title="Disable all add-ins">
    Uncheck every listed add-in and click **OK**.
  </Step>

  <Step title="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.
  </Step>
</Steps>

<Tip>
  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.
</Tip>

***

## 2. Repair the Outlook Profile

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

<Steps>
  <Step title="Open Mail settings">
    Close Outlook. Open **Control Panel → Mail (Microsoft Outlook)** — you can also search for "Mail" in the Start menu.
  </Step>

  <Step title="Open Profile Management">
    Click **Show Profiles**.
  </Step>

  <Step title="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.
  </Step>

  <Step title="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.
  </Step>

  <Step title="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.
  </Step>
</Steps>

<Warning>
  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.
</Warning>

***

## 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.

<Steps>
  <Step title="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.
  </Step>

  <Step title="Locate ScanPST.exe">
    The Inbox Repair Tool is installed with Office. Common locations:

    ```text theme={null}
    # Microsoft 365 / Office 2019 (64-bit)
    C:\Program Files\Microsoft Office\root\Office16\SCANPST.EXE

    # Microsoft 365 / Office 2019 (32-bit on 64-bit Windows)
    C:\Program Files (x86)\Microsoft Office\root\Office16\SCANPST.EXE

    # Office 2016
    C:\Program Files\Microsoft Office\Office16\SCANPST.EXE
    ```

    If you cannot locate it, open File Explorer and search your `C:\` drive for `SCANPST.EXE`.
  </Step>

  <Step title="Locate your data file">
    Your OST or PST file is typically found here:

    ```text theme={null}
    # OST (Exchange / Microsoft 365 accounts)
    C:\Users\<YourUsername>\AppData\Local\Microsoft\Outlook\<account>.ost

    # PST (POP3 or archive)
    C:\Users\<YourUsername>\Documents\Outlook Files\<name>.pst
    ```

    You can also find the exact path in **File → Account Settings → Account Settings → Data Files** tab.
  </Step>

  <Step title="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.
  </Step>

  <Step title="Repair errors">
    If errors are detected, ensure **Make a backup of scanned file before repairing** is checked, then click **Repair**.
  </Step>

  <Step title="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.
  </Step>
</Steps>

<Note>
  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).
</Note>

***

## 4. Clear the Outlook Cache

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

<Steps>
  <Step title="Close Outlook">
    Ensure Outlook is fully closed.
  </Step>

  <Step title="Open the RoamCache folder">
    Press **Win + R**, paste the following path, and press **Enter**:

    ```text theme={null}
    %LocalAppData%\Microsoft\Outlook\RoamCache
    ```
  </Step>

  <Step title="Delete cache files">
    Select all files in this folder (**Ctrl + A**) and delete them. These files are automatically regenerated the next time Outlook launches.
  </Step>

  <Step title="Restart Outlook">
    Open Outlook and allow it to rebuild the cache. Initial load may be slightly slower than usual.
  </Step>
</Steps>

***

## 5. Rebuild the Autocomplete Cache

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

<Steps>
  <Step title="Open the Outlook NK2 / autocomplete cache location">
    Press **Win + R** and enter:

    ```text theme={null}
    %LocalAppData%\Microsoft\Outlook
    ```
  </Step>

  <Step title="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**.
  </Step>

  <Step title="Restart Outlook">
    Outlook will build a fresh autocomplete cache as you send new messages.
  </Step>
</Steps>

<Tip>
  If you need to preserve known-good autocomplete entries before clearing, export the cache using the free **NK2Edit** utility before deleting it.
</Tip>

***

## 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.

<Steps>
  <Step title="Back up your PST files">
    Copy any local PST files (typically in `Documents\Outlook Files`) to a safe location before proceeding.
  </Step>

  <Step title="Remove the existing profile">
    Open **Control Panel → Mail → Show Profiles**, select your current profile, and click **Remove**.
  </Step>

  <Step title="Delete residual cache and config files">
    Press **Win + R** and open:

    ```text theme={null}
    %LocalAppData%\Microsoft\Outlook
    ```

    Delete all files in this folder (your email data on the server is unaffected for Exchange/Microsoft 365 accounts).
  </Step>

  <Step title="Create a fresh profile">
    Return to **Control Panel → Mail → Show Profiles → Add**, and configure your account from scratch using your email address and credentials.
  </Step>

  <Step title="Launch Outlook">
    Open Outlook with the new profile and allow it to complete the initial mailbox synchronization.
  </Step>
</Steps>

***

## Escalation

<Accordion title="When to escalate to your IT Help Desk">
  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).
</Accordion>