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Why is Outlook connection so slow

Anonymous
2025-04-02T09:18:12+00:00

Hi,

My laptop has Office 365 desktop apps installed. When I use any Office desktop app, but Outlook in particular, I receive a a very slow network connection. In Office this is most notable when checking email, viewing calendars, etc. - it takes a long time to complete these actions.

The strange thing is my internet connection is fine otherwise and I have no problems with speed of downloads or speed of any other non-Office apps. The other strange thing is if I connect to a Wifi network outside of my home, I do not have this problem. I have a normal router and I have tried connecting to both 2.4Ghz and 5GHz connection and both have the same problem. Final strange thing - If I use a VPN on my home Wifi then the speed is fine again.

Additonal info:

  • Windows 10 Version 10.0.19045 Build 19045
  • Outlook version: Microsoft® Outlook® for Microsoft 365 MSO (Version 2408 Build 16.0.17928.20336) 64-bit
  • I am connecting to a corporate exchange server.

Any advice on fixing this problem would be much appreciated

Outlook | Windows | Classic Outlook for Windows | For home

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  1. Anonymous
    2025-06-21T08:51:19+00:00

    Hello razer09,

    Thank you for reaching out with these details. The issue you’re experiencing—where Outlook and other Office apps are slow on your home Wi-Fi but work fine elsewhere or with a VPN—suggests a localized network or configuration issue. Here are some steps to troubleshoot:

    1. Check for Network Interference or Restrictions

    • Restart your router/modem: Power cycle your network hardware to clear any temporary glitches.
    • Disable QoS (Quality of Service): Some routers prioritize traffic in ways that may throttle Office 365. Check your router settings and disable QoS if enabled.
    • Check for ISP Throttling: Your ISP might throttle traffic to Exchange servers. The VPN bypassing the issue supports this theory. Contact your ISP to verify.

    2. Configure Outlook/Office for Optimal Performance

    • Disable IPv6:
      • Go to Control Panel > Network and Sharing Center > Change adapter settings.
      • Right-click your Wi-Fi adapter > Properties > Uncheck Internet Protocol Version 6 (TCP/IPv6).
      • Restart Outlook.
    • Update Office: Ensure you’re on the latest build (File > Account > Update Options > Update Now).
    • Disable Add-ins:
      • In Outlook, go to File > Options > Add-ins.
      • Disable all add-ins, restart Outlook, and re-enable one by one to identify conflicts.

    3. Adjust Firewall/Antivirus Settings

    • Temporarily disable your firewall/antivirus to test if they’re interfering. If speed improves, add exceptions for Outlook (outlook.exe) and Office apps.

    4. Test with a Different DNS

    • Try using a public DNS (e.g., Google’s 8.8.8.8 or Cloudflare’s 1.1.1.1):
      • Go to Control Panel > Network and Sharing Center > Change adapter settings > Right-click Wi-Fi > Properties > Select IPv4 > Enter preferred DNS.

    5. Check Exchange Server Connectivity

    6. Reset Network Stack

    Open Command Prompt as admin and run:

    netsh int ip reset
    netsh winsock reset
    ipconfig /flushdns

    Restart your PC afterward.

    If the problem continues after trying these steps, it may be worth escalating to Microsoft Technical Support for deeper investigation. Since you're connecting to a corporate Exchange server, your organization’s IT policies (such as network restrictions or security configurations) could also influence connectivity.

    • Contact your IT team: They can verify if any tenant-level policies are affecting Office 365 performance on certain networks.
    • Microsoft Support via your IT admin: If needed, your organization’s Global Admin can open a case with Microsoft Support. The support team can collect diagnostic logs from your device, analyze them, and provide further troubleshooting steps. You can refer to this article for guidance on creating a service request from the Office 365 Admin Center to receive further assistance: Get support - Microsoft 365 admin | Microsoft Learn.

    Is it possible to write the above in English, please as I didn't understand one word of it?

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  1. Anonymous
    2025-06-27T13:17:41+00:00

    Thanks Chris.

    I disabled IPv6 and this stopped the issue from occurring. Unclear why IPv6 should cause this issue but happy for now that it worked.

    Thanks for the advice

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  2. Anonymous
    2025-04-03T16:23:58+00:00

    Thanks,

    Various things I can try. I do not have admin access so can't do many of them but will check what I can.

    Interestingly, using my phone as a hotspot connected to the same router solves the issue, so it seems direct connection to the router is causing a problem

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  3. Anonymous
    2025-04-02T10:43:33+00:00

    Hello razer09,

    Thank you for reaching out with these details. The issue you’re experiencing—where Outlook and other Office apps are slow on your home Wi-Fi but work fine elsewhere or with a VPN—suggests a localized network or configuration issue. Here are some steps to troubleshoot:

    1. Check for Network Interference or Restrictions

    • Restart your router/modem: Power cycle your network hardware to clear any temporary glitches.
    • Disable QoS (Quality of Service): Some routers prioritize traffic in ways that may throttle Office 365. Check your router settings and disable QoS if enabled.
    • Check for ISP Throttling: Your ISP might throttle traffic to Exchange servers. The VPN bypassing the issue supports this theory. Contact your ISP to verify.

    2. Configure Outlook/Office for Optimal Performance

    • Disable IPv6:
      • Go to Control Panel > Network and Sharing Center > Change adapter settings.
      • Right-click your Wi-Fi adapter > Properties > Uncheck Internet Protocol Version 6 (TCP/IPv6).
      • Restart Outlook.
    • Update Office: Ensure you’re on the latest build (File > Account > Update Options > Update Now).
    • Disable Add-ins:
      • In Outlook, go to File > Options > Add-ins.
      • Disable all add-ins, restart Outlook, and re-enable one by one to identify conflicts.

    3. Adjust Firewall/Antivirus Settings

    • Temporarily disable your firewall/antivirus to test if they’re interfering. If speed improves, add exceptions for Outlook (outlook.exe) and Office apps.

    4. Test with a Different DNS

    • Try using a public DNS (e.g., Google’s 8.8.8.8 or Cloudflare’s 1.1.1.1):
      • Go to Control Panel > Network and Sharing Center > Change adapter settings > Right-click Wi-Fi > Properties > Select IPv4 > Enter preferred DNS.

    5. Check Exchange Server Connectivity

    6. Reset Network Stack

    Open Command Prompt as admin and run:

    netsh int ip reset
    netsh winsock reset
    ipconfig /flushdns

    Restart your PC afterward.

    If the problem continues after trying these steps, it may be worth escalating to Microsoft Technical Support for deeper investigation. Since you're connecting to a corporate Exchange server, your organization’s IT policies (such as network restrictions or security configurations) could also influence connectivity.

    • Contact your IT team: They can verify if any tenant-level policies are affecting Office 365 performance on certain networks.
    • Microsoft Support via your IT admin: If needed, your organization’s Global Admin can open a case with Microsoft Support. The support team can collect diagnostic logs from your device, analyze them, and provide further troubleshooting steps. You can refer to this article for guidance on creating a service request from the Office 365 Admin Center to receive further assistance: Get support - Microsoft 365 admin | Microsoft Learn.
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