Outlook running slow

Try these steps in order to improve Outlook performance when sending/receiving and syncing:

1. Install the latest Windows and Office/Outlook updates
   Out-of-date Outlook or Windows is a common cause of slowness and freezes.
   • Install the latest Windows updates for the version in use (Windows 10/8.1/7, etc.).
   • Then make sure Outlook itself is fully updated as described in How to install the latest applicable updates for Microsoft Outlook (US English only).
2. Check that Outlook isn’t busy with other processes
   Performance can drop significantly if Outlook is:
   • AutoArchiving, or
   • Syncing with a mobile device or other client at the same time. Wait for these operations to complete and see if performance improves.
3. Reduce mailbox and folder size
   Very large mailboxes or folders slow down send/receive and sync.
   • Move items from very large folders into additional folders (for example, split a huge Inbox into subfolders).
   • Use AutoArchive to move older items to an archive file.
   • Optionally reduce data file size using the guidance in Reduce the size of Outlook Data Files (.pst and .ost) and AutoArchive settings explained.
4. Check AppData redirection (if using roaming profiles or network storage)
   If the AppData folder is redirected to a network location, Outlook may freeze while waiting on network I/O.
   • Exit Outlook.
   • Open regedit.exe.
   • Go to:
     HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders
   • Double‑click AppData and set Value data to:
     %USERPROFILE%\AppData\Roaming
   • Select OK and close Registry Editor.
5. Repair Office installation
   Corrupted Office binaries can cause freezing and long send/receive times.
   • Close all Office apps.
   • Open Control Panel → Programs and Features.
   • Right‑click the Microsoft Office installation and choose Repair (or Change → Repair depending on version).
6. Repair Outlook data files (.pst/.ost)
   Corrupted data files can cause slow sync and lockups.
   • Close Outlook.
   • Run the Inbox Repair Tool (SCANPST.EXE) following the steps in Repair Outlook Data Files (.pst and .ost).
7. Check antivirus impact on Outlook
   Outdated or tightly integrated antivirus can slow or freeze Outlook during send/receive.
   • Update antivirus to the latest version from the vendor.
   • If the product has Outlook integration or Outlook add‑ins, temporarily disable that integration or those add‑ins to test performance.
     Note: Changing antivirus settings can increase exposure to threats; only adjust them if comfortable with the risk and consider consulting the antivirus vendor.
8. Create a new Outlook profile
   A corrupted profile can cause freezes and slow operations.
   • Go to Control Panel → Programs → User Accounts → Mail → Show Profiles.
   • Remove the problematic profile.
   • Select Add, name the new profile, and reconfigure the email account.
   • Start Outlook with this new profile and test send/receive.
9. Run the Classic Outlook Advanced Diagnostics troubleshooter
   For classic Outlook on Windows 10 or later, run the Classic Outlook Advanced Diagnostics troubleshooter (SaRA) to automatically check for common configuration and performance issues and get tailored remediation steps.
10. Check for conflicting programs via Selective Startup (advanced)
    Background services or startup programs can interfere with Outlook.
    • Open Control Panel → System and Security → Administrative Tools → System Configuration.
    • On General, choose Selective startup and clear Load startup items (and, for testing, optionally Load system services as described in the article).
    • Restart and test Outlook.
    • Re‑enable services/startup items one by one to identify any that trigger the slowness.

If the environment is Microsoft 365‑based and Outlook remains slow after these steps, follow the same update checks and then apply the additional guidance under Outlook performance is slow in the Microsoft 365 environment, including running the Classic Outlook Advanced Diagnostics and, if applicable, disabling Skype for Business/Lync integration.

References:

• Outlook not responding error or Outlook freezes when you open a file or send mail
• Outlook performance is slow in the Microsoft 365 environment
• Outlook not responding, stuck at "Processing," stopped working, or freezes