Outlook - Performance Issues
Problem
Use this guide when Outlook is slow to open, takes a long time to switch folders, freezes, shows Not Responding, crashes, or closes unexpectedly.
Solution
Before you start:
Save any work in Outlook and close any large apps you do not need. If Outlook is frozen, press Ctrl + Shift + Esc, open Task Manager, select Microsoft Outlook, and choose End task.
Step 1: Restart your computer
A full restart clears temporary issues and stuck Outlook processes.
Save your work.
Restart your computer.
Open Outlook again and test.
If Outlook is still slow or unstable, continue below.
Step 2: Start Outlook in Safe Mode
Safe Mode opens Outlook without COM add-ins. If Outlook works normally in Safe Mode, an add-in is a likely cause of the problem. Microsoft specifically recommends Safe Mode to check whether add-ins are causing crashes, hangs, or poor performance.
Close Outlook.
Press Windows key + R.
Type outlook /safe
Press Enter.
Choose your profile if prompted.
If Outlook works better in Safe Mode
Disable add-ins:
In Outlook, select File
Select Options
Select Add-ins
At the bottom, next to Manage, choose COM Add-ins
Select Go
Clear the check boxes for add-ins you do not need
Select OK
Restart Outlook normally
Try disabling nonessential add-ins first, then testing again.
Step 3: Repair Microsoft 365 Apps
If Outlook is still unstable, repair the Office installation. Microsoft says repairing Office can resolve Outlook freezing and not-responding issues, and that Online Repair is the most complete option.
Close all Office apps.
Open Settings.
Go to Apps > Installed apps.
Select Microsoft 365 apps
Click on the 3 dots then choose Modify.
Run Quick Repair first if available
If the issue continues, run Online Repair
Online Repair may take longer and may require you to sign in again afterward.
Step 4: Create a New Outlook Profile
You can remove your current profile and create a new one by following the instructions found here.
Step 5: Check for Large Mail Folders or a Large Outlook Data File
Large Outlook data files can cause pauses, and folders with very high item counts can slow Outlook, especially when switching folders. Folders with more than 100,000 items can be slower and large .ost files may cause pauses as they grow.
Try these cleanup steps:
Empty Deleted Items
Empty Junk Email
Move older mail out of your Inbox into subfolders or archive folders
Reduce very large folders with tens of thousands of items
Keep Outlook sorted by Date in large folders, since other views can be slower in very large folders.
Step 6: Repair Outlook Data Files
If Outlook says there is a problem with your mailbox data file, or Outlook started acting up after Outlook or Windows closed suddenly, the file may need to be repaired. There is a built-in tool called the Inbox Repair Tool to fix these files. If an Outlook data file did not close properly, Outlook may run slowly or act strangely until it finishes checking and fixing the file in the background.
Use this step only if:
Outlook shows an error about opening the data file
Outlook says folders cannot be opened
Helpdesk instructs you to repair the file
If needed, the tool is called Inbox Repair Tool (SCANPST.EXE) which can repair the .pst files.
Step 7: Run Microsoft’s Built-In Troubleshooting Tools
Microsoft provides troubleshooting tools through the Get Help app for many Microsoft 365 issues, including Outlook-related scenarios.
Open the Get Help app in Windows
Search for Microsoft 365 or Outlook troubleshooting
Follow the prompts