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CAA20002 Severity: High

Could not connect to Microsoft servers

Teams reports CAA20002 during sign-in. Usually caused by a blocked network, outdated TLS settings, or a corrupted token cache.

Last verified:

Affected systems

windows macos

Symptoms

  • Sign-in fails with CAA20002
  • Teams hangs on the login screen
  • Other Microsoft services in the browser keep working

Possible causes

  • Cache full of expired auth tokens
  • Active VPN or proxy blocks login.microsoftonline.com
  • TLS 1.2 disabled on the machine (rare, mostly Windows 7 legacy)
  • Wrong date or timezone setting

Solutions

1.Clear the Teams cache fully

  1. Quit all Teams processes via Task Manager or Activity Monitor.

  2. Delete the cache folder.

    %appdata%\Microsoft\Teams
    ~/Library/Application Support/Microsoft/Teams

  3. For the new client, also delete this folder.

    %localappdata%\Packages\MSTeams_8wekyb3d8bbwe\LocalCache
    ~/Library/Group Containers/UBF8T346G9.com.microsoft.teams

  4. Restart Teams and sign in fresh.

2.Disable VPN and test proxy

  1. Disconnect the VPN tunnel and try sign-in without it.

  2. If your company uses a proxy, verify login.microsoftonline.com and teams.microsoft.com are reachable.

  3. Microsoft lists the endpoints at https://learn.microsoft.com/microsoft-365/enterprise/urls-and-ip-address-ranges

  4. Ask IT to allowlist the Microsoft 365 endpoints if needed.

3.Verify TLS 1.2 (Windows only)

Windows

  1. Open 'Internet Options' (inetcpl.cpl) via Run.

  2. Advanced tab, ensure 'Use TLS 1.2' and 'Use TLS 1.3' are enabled.

  3. Apply and reboot.

4.Verify date and time

Windows

  1. Settings, Time and Language, Date and Time.

  2. Enable automatic time and timezone sync.

  3. Click 'Sync now'.

macOS

  1. System Settings, General, Date and Time.

  2. Enable 'Set date and time automatically'.

  3. Set timezone to 'Automatic' as well.

Background

CAA20002 is almost always a client-side issue, not a server outage. If your account works fine on office.com in a browser, the cache reset fixes more than 80 percent of cases. If it also fails there, it is the network or account, not the Teams client.

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