Summary

This article covers what to do when Outlook freezes mid-use, displays "(Not Responding)" in the title bar, or stops reacting to clicks and keyboard input. These steps address the most common causes — stuck background processes, misbehaving add-ins, oversized mailboxes, and corrupted data files — and most take less than two minutes.

This guide is for classic Outlook. New Outlook for Windows is a separate application: Microsoft does not support COM add-ins or RSS feeds in it, it does not support multiple mail profiles, and it puts the offline-mail setting under Settings > General > Offline rather than in a File menu. Most of the steps below have nothing for a New Outlook reader to click. Use the toggle in the top-right corner of the window to go back to the classic app — How to Switch Between New Outlook and Classic Outlook on Windows covers both directions, and Understanding the Missing Features in "New" Outlook covers what else changed.

Symptoms

• Outlook is frozen and does not react to clicks or typing.
• The title bar shows "(Not Responding)" next to the window name.
• Outlook is stuck and won't close, no matter what you click.

In this guide

• 1. Wait 15 Seconds Before Doing Anything
• 2. Force-Close and Restart Outlook
• 3. Start Outlook in Safe Mode
• 4. Identify and Disable the Problem Add-In
• 5. Reduce Mailbox Size
• 6. Reduce the Cached Mailbox Window
• 7. Disable RSS Feeds and Unnecessary Features
• 8. Repair Your Office Installation
• 9. Create a Fresh Outlook Profile
• 10. When to Contact IT

Before You Start

• A working internet connection (verify by opening a web page in your browser).
• The classic Outlook desktop app. If your window has a New Outlook toggle switched on, the menus below will not match what you see — see the note at the top of this page.

Instructions

1. Wait 15 Seconds Before Doing Anything

Not every frozen Outlook is actually frozen.

When Outlook shows "(Not Responding)," it is often processing a large operation in the background — syncing a folder, indexing email, or downloading attachments. Windows labels any app as "Not Responding" if it has not replied to input for a few seconds, even if it is still working.

1. Wait at least 15 seconds without clicking anywhere in the Outlook window.
2. Watch the status bar at the bottom of Outlook. If it shows a progress indicator (e.g., "Updating inbox..." or a folder sync bar), Outlook is still working — let it finish.
3. If Outlook recovers on its own, the freeze was temporary. If it happens frequently, continue with the steps below to find the root cause.

2. Force-Close and Restart Outlook

If Outlook remains frozen after 30 seconds, a clean restart clears any stuck process.

1. Press Ctrl + Shift + Esc to open Task Manager.
2. Find Microsoft Outlook in the list. It may show (Not Responding) next to it.
3. Click it and select End task.
4. Wait 10 seconds, then reopen Outlook from the Start menu or taskbar.
5. If Outlook opens normally and the freeze does not recur, the issue was a one-time stuck process. If it freezes again, continue to Step 3.

3. Start Outlook in Safe Mode

Safe Mode launches Outlook with all add-ins disabled. If Outlook runs smoothly in Safe Mode, an add-in is causing the freeze.

1. Close Outlook completely (use Step 2 if it is frozen).
2. Press Win + R to open the Run dialog.
3. Type outlook.exe /safe and press Enter.
4. Outlook opens with "[Safe Mode]" in the title bar.
5. Use Outlook for a few minutes — switch folders, open emails, run a search.
6. If the freeze does not happen in Safe Mode, an add-in is the cause. Continue to Step 4.
7. If the freeze still happens in Safe Mode, the problem is not add-in related. Skip to Step 5.

4. Identify and Disable the Problem Add-In

Add-ins from antivirus software, CRM tools, and PDF converters are frequent causes of Outlook freezing.

1. Open Outlook normally (not in Safe Mode).
2. Go to File > Options > Add-ins.
3. At the bottom, next to Manage, select COM Add-ins and click Go.
4. You will see a list of all installed add-ins with checkboxes.
5. Uncheck all add-ins and click OK.
6. Restart Outlook and use it normally for 10–15 minutes.
7. If the freeze is gone, one of the disabled add-ins was the cause. Re-enable them one at a time, restarting Outlook after each, until the freeze returns — that add-in is the culprit.
8. Leave the problem add-in disabled. If it is a business-critical tool, raise a ticket naming the add-in and the version shown in File > Options > Add-ins, and ask IT to install a build that works with your Outlook version.

5. Reduce Mailbox Size

Large mailboxes — especially those near the 50 GB or 100 GB limit — force Outlook to index and sync massive amounts of data, which causes freezing.

1. Go to File > Info and look at the Mailbox Settings section. A storage bar shows how full your mailbox is.
2. If your mailbox is above 80% full, reduce its size:
   • Delete old emails you no longer need (especially those with large attachments).
   • Empty the Deleted Items folder — deleted emails still count toward your quota.
   • Empty the Junk Email folder.
3. To find the largest emails: go to your inbox, click the Filter icon, and sort by Size (largest first) or search for size:>10MB.
4. After cleaning up, Outlook may take a few minutes to re-sync. The freezing should improve significantly.

6. Reduce the Cached Mailbox Window

Outlook downloads and stores a local copy of your emails for offline access. The more email it caches locally, the larger the local data file — and the more likely Outlook is to freeze.

New Outlook for Windows: this slider does not exist. The equivalent is Settings > General > Offline > Days of email to save, where the dropdown offers 7, 30, 90 or 180 days.

1. Go to File > Account Settings > Account Settings.
2. On the Email tab, select your account and click Change.
3. Look for the slider labeled Download email for the past or Mail to keep offline.
4. Reduce the value. If it is set to All, change it to 12 months or 6 months.
5. Click Next > Done.
6. Outlook will remove older items from the local cache (they remain accessible on the server and in Outlook on the web). This reduces the data file size and improves performance.

7. Disable RSS Feeds and Unnecessary Features

Outlook's built-in RSS reader and other background features consume resources and can cause freezing, especially on older hardware.

1. Go to File > Options > Advanced.
2. Scroll down to the RSS Feeds section.
3. Uncheck Synchronize RSS Feeds to the Common Feed List (CFL) in Windows.
4. Scroll further to the Other section.
5. Uncheck Enable logging (troubleshooting) if it is checked.
6. Under the Display section, consider unchecking Disable hardware graphics acceleration — try both settings and see which one performs better on your machine.
7. Click OK and restart Outlook.

8. Repair Your Office Installation

If Outlook continues to freeze after addressing add-ins and mailbox size, the Outlook program files themselves may be corrupted.

1. Close Outlook completely.
2. Press the Start key, type Installed Apps, and press Enter.
3. Search for Microsoft 365 (or Office).
4. Click the … (three dots) next to it and select Modify.
5. Select Quick Repair and click Repair. This takes 5–10 minutes and does not require internet.
6. Open Outlook and test. If the freezing continues, repeat the process and select Online Repair instead (this takes 15–30 minutes and requires internet, but is more thorough).

9. Create a Fresh Outlook Profile

If repair does not help, the Outlook profile or its local data file (OST) may be corrupted beyond repair. Creating a new profile forces Outlook to build a fresh local copy of your mailbox.

1. Close Outlook completely.
2. Press Win + R, type control, and press Enter to open Control Panel.
3. Search for Mail and open Mail (Microsoft Outlook).
4. Click Show Profiles.
5. Click Add and name the new profile (e.g., NewProfile).
6. Follow the prompts to sign in with your work email address.
7. Select Always use this profile and choose the new profile from the drop-down.
8. Click OK and open Outlook. It will create a new data file and re-download your mailbox from the server.

10. When to Contact IT

The local fixes are exhausted by this point, so the ticket needs what IT cannot see from their side. Give the exact wording of any Exchange connectivity or certificate error, how long each freeze lasts, and confirmation that it still happens in Safe Mode on a new profile after an Online Repair.

Contact your IT helpdesk if:

• Outlook freezes in Safe Mode and after a full Online Repair — the issue may be related to your mailbox configuration on the server.
• Creating a new Outlook profile did not resolve the freezing.
• Outlook freezes only when opening emails from specific senders or with specific attachment types — this could indicate a security concern.
• Multiple colleagues are experiencing the same freezing at the same time — this may indicate a server-side or network issue.
• You receive errors about Exchange connectivity or certificate warnings during the freeze.

Troubleshooting

DANGER

If Outlook works without freezing in Safe Mode (outlook.exe /safe), the cause is almost certainly an add-in. Focus on Step 4. If it freezes even in Safe Mode, focus on mailbox size (Step 5), cache reduction (Step 6), and repair (Step 8).

Symptom / Error	Potential Cause	Solution
"(Not Responding)" for 5–10 seconds, then recovers	Large folder sync or indexing	Reduce cache window (Step 6) and check mailbox size (Step 5).
Freezes every time you open a specific folder	Corrupted item in that folder	Open Outlook on the web, move items from that folder, then try again.
Freezes when searching	Search index rebuilding	Wait for indexing to complete, or reduce cached mailbox window (Step 6).
Freezes immediately on startup	Stuck profile or corrupted data file	Start in Safe Mode (Step 3). If Safe Mode works, create a new profile (Step 9).
Freezes only with a specific add-in enabled	Add-in compatibility issue	Disable the add-in (Step 4). Report the issue to IT if it is required for your work.
Freezes after a Windows update	Office compatibility issue	Run Online Repair (Step 8).
"Outlook is using a lot of memory" warning	Oversized local data file	Reduce cache window (Step 6) and clean up mailbox (Step 5).

Related Articles

• How to Fix Outlook Not Opening or Crashing on Startup
• How to Fix Outlook Emails Not Syncing
• How to Fix Outlook Not Receiving Emails (Mailbox Over Size Limit)
• How to Fix Outlook Search Not Finding Emails
• How to Use Outlook Categories and Flags to Stay Organized
• How to Fix Common Computer Glitches by Restarting
• How to Fix Slow Performance on Windows 11

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