Slow performance in Outlook

Troubleshooting Slow Performance in Outlook (Microsoft 365)

Symptoms

You may notice:

• Outlook is slow to open or respond to emails.
• Emails remain in the Outbox for a long time.
• Attaching files takes longer than expected.
• You see messages like “Outlook is retrieving information from the server.”

Causes

Performance issues may be caused by:

• Large mailbox or data files (.pst/.ost).
• Outdated Outlook version or missing updates.
• Third-party add-ins.
• Network latency or proxy/firewall issues.
• Antivirus software interference.
• High item count in folders.

Resolution Steps

1. Install the Latest Outlook Updates

Ensure Outlook is fully updated:

• Open Outlook.
• Go to File > Office Account > Update Options > Update Now.

2. Check for Large Data Files

• Large .pst or .ost files can slow Outlook.
• Files over 10 GB may cause frequent pauses.
• Archive old emails or split folders with over 100,000 items .

3. Disable Unnecessary Add-ins

• Open Outlook in Safe Mode: Outlook /safe
• Go to File > Options > Add-ins > COM Add-ins > Go
• Uncheck non-essential add-ins and restart Outlook .

4. Check Antivirus and Logging

• Temporarily disable antivirus integration with Outlook (if safe to do so).
• Turn off logging: Window > Sync Errors > Action > Uncheck logging 

5. Repair Office Installation

• Go to Control Panel > Programs > Uninstall a Program
• Select Microsoft 365 > Change > Online Repair .

6. Create a New Outlook Profile

• Go to Control Panel > Mail > Show Profiles
• Remove the old profile (if safe) and create a new one.