Can't sign in or activate Outlook and Microsoft 365 applications

  • Article
  • Applies to:
    Outlook for Microsoft 365, Outlook 2019, Outlook 2016, Outlook 2013

Symptoms

Microsoft Outlook or other office applications can't complete activation or can't connect to Exchange Online or other Microsoft 365 services.

The wired LAN network connection may display a yellow exclamation mark alert that indicates "No Internet Access".

Note

This issue doesn't occur when you use Wi-Fi.

Cause

This issue occurs because of either of the following reasons:

  • The Network Interface Card (NIC) drivers are incompatible.
  • The IPv4 Checksum functionality is active.

Resolution

Step 1: Update the network card drivers on your device

Network card manufacturers frequently release driver updates to improve performance and fix compatibility issues. If there is no update available through Windows Update, go to the support or download section of your network card manufacturer's website to learn how to download and install the latest driver.

If an updated driver doesn't fix this issue, go to Step 2.

Step 2: Test by disabling the IPv4 Checksum Offload feature

Note

This step may resolve the issue only temporarily. Work with the network device manufacturer and Microsoft Windows support to find a permanent solution.

Here's how to disable the IPv4 Checksum Offload feature:

  1. In Windows Control Panel, open the View network connections item.
  2. Right-click the network adapter, select Properties > Configure, and then select the Advanced tab.
  3. Select IPv4 Checksum Offload, and then select Disable.
  4. Select OK to save the changes.

More information

Address checksum offloads are a NIC feature that offloads the calculation of address checksums (IP, TCP, UDP) to the NIC hardware for both send (Tx) and receive (Rx).

On the receive path, the checksum offload calculates the checksums in the IP, TCP, and UDP headers and indicates to the operating system whether the checksums passed, failed, or weren't checked. If the NIC asserts that the checksums are valid, the system accepts the packet unchallenged. If the NIC asserts that the checksums are invalid or not checked, the IP/TCP/UDP stack internally calculates the checksums again. If the computed checksum fails, the packet is discarded.

For more information, see Hardware Only (HO) features and technologies.