How to Fix Outlook Running Slow on Windows

What Causes This?

Outlook usually runs slow when its local data files get too large, add-ins pile up, or Windows is under strain from too many background apps and temporary files. A damaged Outlook profile, a bloated mailbox cache, or search indexing problems can also cause delays when opening emails, switching folders, or searching. In some cases, outdated Office or Windows updates are part of the problem too.

Common Symptoms

• Outlook takes a long time to open or close
• Emails load slowly or freeze when you click them
• Search results are delayed or incomplete
• Outlook shows “Not Responding” often
• Typing, scrolling, or switching folders feels laggy

How to Fix It Manually

1. Restart Outlook and check Task Manager

   • Close Outlook completely.
   • Press Ctrl + Shift + Esc to open Task Manager.
   • In the Processes tab, look for Microsoft Outlook.
   • If it is still running after you closed it, select it and click End task.
   • Restart Outlook and see if performance improves.

2. Start Outlook in Safe Mode to test add-ins

   • Press Windows + R to open Run.
   • Type outlook.exe /safe and press Enter.
   • If Outlook is faster in Safe Mode, an add-in is likely causing the slowdown.
   • To disable add-ins:
     1. In Outlook, click File > Options > Add-ins.
     2. At the bottom, next to Manage COM Add-ins, click Go.
     3. Uncheck unnecessary add-ins and click OK.
     4. Restart Outlook normally.

3. Reduce mailbox size and clean up old items

   • In Outlook, go to File > Tools > Mailbox Cleanup.
   • Use View Mailbox Size to see if your mailbox is very large.
   • Empty the Deleted Items folder and archive or delete old messages with large attachments.
   • If you use POP or local PST files, keeping them smaller can noticeably improve speed.

4. Repair the Outlook data file

   • Close Outlook.
   • Use File Explorer to find the Outlook Inbox Repair Tool, usually called SCANPST.EXE.
   • Common locations include:
     • C:\Program Files\Microsoft Office\root\Office16\
     • C:\Program Files (x86)\Microsoft Office\root\Office16\
   • Open SCANPST.EXE, browse to your Outlook data file, and run the repair.
   • Your Outlook files are often in:
     • C:\Users\YourName\AppData\Local\Microsoft\Outlook\

5. Rebuild Windows Search indexing

   • Open Start, type Indexing Options, and open it.
   • Click Advanced.
   • Under Troubleshooting, click Rebuild.
   • This can help if Outlook search is slow or missing results.
   • Let indexing finish, then test Outlook again.

6. Update Office and Windows

   • In Outlook, go to File > Office Account > Update Options > Update Now.
   • Then open Settings > Windows Update and click Check for updates.
   • Install available updates and restart your PC.

7. Reduce background strain in Windows

   • Open Task Manager with Ctrl + Shift + Esc.
   • Check for apps using high CPU, Memory, or Disk.
   • Close programs you do not need, especially browsers with many tabs, cloud sync tools, or other Office apps.
   • You can also clear temp files by opening Settings > System > Storage > Temporary files and removing unnecessary items.

Fix It Automatically with Kudu

If Outlook is slow because Windows is overloaded with temporary files, startup clutter, or background processes, Kudu can help fix that without all the manual digging. It scans for common PC slowdowns, removes junk files, and reduces system strain so apps like Outlook have more resources to run smoothly.

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