Outlook is working very slow...emails dont download even for days

Since mail works normally in mobile and webmail, the mailbox itself is likely fine. The issue is most likely with classic Outlook on Windows, local network conditions, or Outlook configuration.

Try this in order:

1. Check Microsoft 365 service health If this is a Microsoft 365 account, an admin should sign in to the Microsoft 365 portal and check Service health. If there is an Exchange Online incident, Outlook performance can be slow until the service issue is resolved.
2. Check for local network issues Slow Outlook can be caused by local proxy, firewall, or ISP/network problems even when other clients appear better.
3. Install the latest Outlook updates Make sure Outlook and Windows are fully updated. Out-of-date Office or Windows files can cause hangs, slow send/receive, and poor performance.
4. Wait if Outlook is busy in the background In classic Outlook, check the status bar at the bottom. If Outlook is processing a large attachment, send/receive, AutoArchive, or another mailbox task, wait 2–3 minutes and see whether it recovers.
5. Reduce folder load Large folders can slow Outlook significantly.
   • Move older items out of very large folders such as Inbox, Sent Items, or other busy folders.
   • Archive older items if needed.
   • Empty Deleted Items/Trash.
6. Change sorting in slow folders If a folder opens slowly, sort by a faster field:
   • For mail, use Date Received or Subject.
   • For contacts, use Name.
7. Turn off Outlook logging if enabled Logging can slow Outlook.
   • Open Window > Error Log or Sync Errors
   • Select the Action button
   • Clear Turn on logging for troubleshooting
   • Restart Outlook
8. Disable Skype for Business / presence integration This integration can affect Outlook performance.
   • In Outlook: File > Options > Contacts
   • Clear Display online status next to a name
   • Restart Outlook
9. Run the Classic Outlook Advanced Diagnostics troubleshooter Use the Classic Outlook Advanced Diagnostics troubleshooter in Get Help to generate a detailed configuration report. This applies to classic Outlook on Windows, not new Outlook.
10. Check whether AppData is redirected to a network location If Outlook data such as signatures or dictionaries is stored through redirected AppData on a slow network, Outlook can become very slow. Registry changes are risky and can cause serious problems if done incorrectly. Back up the registry first before changing AppData redirection settings.

If the main symptom is that messages stay unsent or downloading is delayed for days, start with service health, updates, large folder cleanup, and Skype/presence integration disablement first. Those are the most directly supported checks for this scenario.

• Outlook performance is slow in the Microsoft 365 environment
• Outlook is running slow
• Plan and configure Cached Exchange Mode in Outlook 2016 for Windows
• Outlook for Windows not responding, hangs, freezes, or stops working
• How to troubleshoot performance issues in Outlook
• Outlook not responding error or Outlook freezes when you open a file or send mail