Outlook fails to connect to proxy server autodiscover


Some Microsoft Outlook users after upgrading to Windows 11 started reporting that they noticed that some versions of Outlook, including Outlook for Microsoft 365 on their system that connected to the internal Exchange server, no longer work with the error message. Outlook fails to connect to proxy server autodiscover. This article provides the most applicable solutions to the problem.

When this problem occurs, you receive the following error message complete with error code;

Microsoft Outlook
There is a problem with the proxy server’s security certificate.
Outlook fails to connect to proxy server autodiscover. (Error code 80000000).

Outlook fails to connect to proxy server autodiscover

If you are faced with the Outlook fails to connect to proxy server autodiscover problem on your Windows 11/10 device, you can try our recommended solutions below in no particular order to fix the problem on your system.

  1. Initial checklist
  2. Enable TLS 1.0 on local Windows 11 machine
  3. Add TLS 1.2 to Exchange Server
  4. Upgrade Exchange Server

Let’s take a look at the description of the process involved regarding each of the listed solutions.

1]Initial checklist

Before trying the solutions below, you can do the following and after each task, see if Outlook can now connect to proxy server autodiscovery without issue:

  • Check Outlook client compatibility with Exchange server version. For example, Microsoft 365 is not supported for Exchange 2010. If there is a problem when using Microsoft 365 and Exchange 2010, the incompatibility can also impact that. In this case, install the corresponding compatible Outlook client such as Outlook 2013. Also, to further confirm if the problem is related to Outlook client, you can try to log in to Outlook Web App (OWA) and check if it works normally.
  • Check if the Autodiscover service is running. Since the issue in question is related to Autodiscover, you can follow the instructions in this article to test Autodiscover connectivity using the Outlook client. Also, make sure that your PC is not having internet connectivity issues and that the Exchange server is not offline.
  • On-premises users can run Microsoft Remote Connectivity Analyzer and Office 365 users can run Microsoft Support and Recovery Assistant.
  • You can add your Exchange server name/MX record to the proxy exclusion list and see if that helps. You can also try using a VPN locally on your network.

2]Enable TLS 1.0 on local Windows 11 machine

Enable TLS 1.0 Registry Editor

This is more of a workaround than a solution. However, this action is not recommended because TLS 1.0 is retired and needs to be moved. However, if you need an immediate resolution to the highlighted issue, you can enable or enable TLS 1.0 through the registry on the local Windows 11 machine. Proceed as follows:

Since this is a registry operation, it is recommended to backup the registry as a necessary precautionary measure. Once done, you can proceed as follows:

HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionInternet SettingsWinHttp
  • In the location, in the right pane, double-click the Default secure protocols enter to modify its properties.

If the key is not present, right-click on the empty space in the right pane, then select New > DWORD (32-bit) value to create the registry key, then rename the key accordingly and press Enter.

  • Double-click the new entry to edit its properties.
  • Type 00000080 in the Vvalue data domain.
  • Click on OKAY or press Enter to save the change.
  • Next, navigate to the registry path below and repeat the steps above:
HKEY_LOCAL_MACHINESOFTWAREWow6432NodeMicrosoftWindowsCurrentVersionInternet SettingsWinHttp
  • Quit Registry Editor when you’re done.
  • Restart the computer.

3]Add TLS 1.2 to Exchange Server

Windows 11 disables TLS 1.0 and TLS 1.1 by default and Exchange 2010 running on Windows 2008 R2 uses TLS 1.0. As noted in some cases, the problem in sight started when Windows 10 client machines were upgraded to Windows 11 and the problem is only noticed on workstations connected outside of the subnet the server is on connected. That is, all workstations connected to the same subnet as the server worked fine after Windows 11 upgrade, but all workstations outside of that subnet failed with the proxy (error code 80000000).

This is a safe workaround to the problem and the IT admin should add TLS 1.2 to the Exchange servers and then restart the server afterwards. This works because Windows 11 supports TLS 1.2 by default.

Below are the registry keys that can be added through the command prompt:

[HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlSecurityProvidersSCHANNELProtocolsTLS 1.2Client]
  • Added DWORD: DisabledByDefault = 00000000 (0)
  • DWORD added: Enabled = 00000001 (1)
[HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlSecurityProvidersSCHANNELProtocolsTLS 1.2Server]
  • Added DWORD: DisabledByDefault = 00000000 (0)
  • DWORD added: Enabled = 00000001 (1)
  • Added DWORD: SystemDefaultTlsVersions=00000001 (1)
  1. Added DWORD: SystemDefaultTlsVersions=00000001 (1)

4]Upgrade Exchange Server

For example, Exchange Server 2010 reached its end of support on October 13, 2020. For a better user experience, it is recommended that you upgrade your Exchange server to a newer version by your Internet Service Provider (ISP) or the corporate mail server or IT department. administrator. After upgrading Exchange, you can upgrade and reinstall the latest version of Outlook client for Windows 11/10.

I hope this post helps you!

Why does Outlook say Unable to connect to proxy server?

This issue may occur if one or more of the following conditions are true:

  • Connecting to the server requires a Certificate Authority (CA).
  • You did not trust the CA at the root.
  • The certificate may be invalid or revoked.

What does proxy email mean?

A mail proxy server is a standalone machine located in front of the actual mail server. The mail proxy server is customized to provide some or all of the following services: Web-based email via IMAP.


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