Outlook loads very slowly when started

For classic Outlook on Windows, slow startup and very slow send/receive can be caused by a service issue, local network issues, mailbox size, Outlook integration features, or client-side configuration problems.

Use this order:

1. Check for a Microsoft 365 service issue
   • If the mailbox is in Microsoft 365, an Exchange Online issue can cause Outlook to open messages slowly, leave mail in Outbox, or show “Outlook is retrieving information from the server.”
   • In the Microsoft 365 portal, open Service health to see whether there is an active service incident.
2. Check local network conditions
   • Slow proxy, firewall, ISP, or other local network problems can slow Outlook startup and send/receive.
   • If possible, test on a different network to confirm whether the delay is network-related.
3. Install the latest Outlook updates
   • Make sure the latest Outlook updates are installed, then test again.
4. Reduce large folders and mailbox load
   • Large folders can cause performance issues when Outlook opens folders or processes mail.
   • Move older items from very large folders into separate folders, or archive them with AutoArchive.
   • If a folder is slow because of sorting, use common sort fields instead. Faster fields include:
     • Contacts: Name
     • Mail: Date Received or Subject
5. Turn off Outlook and Skype presence integration
   • In Outlook, go to File > Options > Contacts.
   • Clear Display online status next to a name under Online status and photographs.
   • Restart Outlook.
   • In some Microsoft 365 environments, Skype for Business/Lync integration can affect Outlook performance.
6. Run the Classic Outlook Advanced Diagnostics troubleshooter
   • Run the Classic Outlook Advanced Diagnostics troubleshooter in Get Help.
   • It creates a detailed configuration report and can provide additional resolution steps.
   • This troubleshooter does not work in new Outlook for Windows.
7. Check whether AppData is redirected to a network location
   • Outlook stores some data in AppData. If that folder is redirected to a slow network location, startup and general performance can degrade.
   • Changing this requires a registry edit.
   • Warning: incorrect registry changes can cause serious problems. Back up the registry first.
   • The documented setting is:
     • Registry key: HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders
     • Value: AppData
     • Data: %USERPROFILE%\AppData\Roaming

If the issue started right after updates, also check whether the mailbox is a POP account and whether Windows update KB5074109 is installed. A known issue can cause classic Outlook POP profiles to hang or freeze after that update. In that case, uninstalling that update has been reported as a workaround, but this reduces security posture temporarily and should be coordinated carefully in managed environments.

• Outlook performance is slow in the Microsoft 365 environment
• Outlook is running slow
• Outlook not responding error or Outlook freezes when you open a file or send mail
• How to troubleshoot performance issues in Outlook
• Outlook stalls - Microsoft Q&A
• I cannot send mails through outlook - Microsoft Q&A