Outlook performance is slow in the Microsoft 365 environment


When you use Microsoft Outlook together with Microsoft 365, you experience one or more of the following symptoms:

  • Outlook responds slowly when you try to open email messages.
  • When you send an email message, the message sits in the Outbox folder for a long time.
  • Outlook responds slowly when you try to insert an attachment. Frequently, you receive the following warning message:

    Outlook is retrieving information from the server


This issue may occur for many reasons.

This issue may be caused by an Exchange Online server issue. In this case, sign in to the Microsoft 365 portal by using your administrator credentials, and then select service health to determine whether other customers are experiencing the same issue. If other customers are experiencing the issue, the issue should end when the service-interrupting event is resolved.

Also, determine whether any local network issues might be causing the problem. This includes issues that affect your local proxy server, firewall, or Internet service provider.


To fix this issue, follow these steps:

  1. Make sure that the latest updates for Outlook are installed. For more information, see How to install the latest applicable updates for Microsoft Outlook (US English only).

    Test to learn whether the issue is resolved. If the issue persists, go to step 2.

  2. Try the methods from the following articles, as appropriate for the version of Outlook that you're running:

    If the issue persists, go to step 3.

  3. Try the following:

    • Select Outlook Advanced Diagnostics, and then select Run when you are prompted by your browser.


      This diagnostic creates detailed information about your Outlook configuration and provides solutions for any known issues that are detected. It also gives you the option to upload your results to Microsoft so that a Support engineer can review them before you make a Support call.

    • Disable Skype for Business Online (formerly Lync Online) integration. If Outlook is integrated with Skype for Business Online in your Microsoft 365 environment, the integration may affect Outlook's performance. To disable Skype for Business Online integration with Outlook, follow these steps:

      1. Open Lync, select the gear icon in the upper-right corner, point to Tools, and then select Options.
      2. Select Personal, and then clear the check boxes in the Personal information manager area.
      3. Select OK, and then restart Outlook and Lync.

Still need help? Go to Microsoft Community.