Outlook is unable to connect to the proxy server autodiscover

Some Microsoft Outlook users after upgrading to Windows 11 started reporting they noticed that some versions of Outlook including Outlook for Microsoft 365 on their system that used to connect to the internal Exchange server no longer works with the error message Outlook is unable to connect to the proxy server autodiscover. This post provides the most applicable solutions to the issue.

When this issue occurs, you’ll receive the following full error message with error code;

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

Outlook is unable to connect to the proxy server autodiscover

If you’re faced with the Outlook is unable to connect to the proxy server autodiscover issue on your Windows 11/10 device, you can try our recommended solutions below in no particular order to resolve the issue on your system.

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

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

1] Initial checklist

Before you try the solutions below, you can do the following and after each task see if Outlook can now connect to the proxy server autodiscover without issues:

• Check Outlook client compatibility with Exchange server version. For example, Microsoft 365 is not supported for Exchange 2010. If there’s something wrong when you use Microsoft 365 and Exchange 2010, incompatibility may also have an impact on this. In this case, install the corresponding compatible Outlook client, such as Outlook 2013. In addition, to further confirm whether the issue is related to Outlook client, you can try logging in to Outlook Web App (OWA) and check if it works normally.
• Check if Autodiscover service is running.  As the issue in focus is related to Autodiscover, you can follow the instructions in this post to test Autodiscover connectivity using the Outlook client. In addition, make sure your PC is not experiencing 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’s MX name/record to proxy exclusion list and see if that helps. Also, you can try using a VPN locally on your network.

2] Turn on TLS 1.0 on the local Windows 11 machine

This is more of a workaround than a solution. However, this action is not recommended because TLS 1.0 is retired and should be moved away from. Nevertheless, if you need an immediate resolution to the issue in highlight you can enable or turn on TLS 1.0 via the registry on the local Windows 11 machine. Do the following:

Since this is a registry operation, it is recommended that you back up the registry as necessary precautionary measures. Once done, you can proceed as follows:

• Press Windows key + R to invoke the Run dialog.
• In the Run dialog box, type regedit and hit Enter to open Registry Editor.
• Navigate or jump to the registry key path below:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\WinHttp

• At the location, on the right pane, double-click the DefaultSecureProtocols entry to edit its properties.

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

• Double-click on the new entry to edit its properties.
• Type 00000080 in the Value data field.
• Click OK or hit Enter to save the change.
• Next, jump to the registry path below and repeat the steps as above:

HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Internet Settings\WinHttp

• Exit Registry Editor when done.
• Restart computer.

3] Add TLS 1.2 to the 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 reported in some cases, the issue in view started when the Windows 10 client machines were upgraded to Windows 11 and the issue is only noticed on workstations connected outside of the subnet the server is connected to. That is all of the workstations connected to the same subnet as the server was working fine after the Windows 11 upgrade, but all of the workstations outside of that subnet failed with proxy (Error Code 80000000).

This is a safe workaround to the issue and it requires the IT admin to add TLS 1.2 to the Exchange servers and then reboot the server afterward. This works because Windows 11 supports TLS 1.2 by default.

Below are the registry keys that can be added via Command Prompt:

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2\Client]

• Added DWORD: DisabledByDefault = 00000000 (0)
• Added DWORD: Enabled = 00000001 (1)

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2\Server]

• Added DWORD: DisabledByDefault = 00000000 (0)
• Added DWORD: Enabled = 00000001 (1)

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft.NETFramework\v2.0.50727]

• Added DWORD: SystemDefaultTlsVersions = 00000001 (1)

[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft.NETFramework\v2.0.50727]

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 your better user experience, it is recommended that you upgrade your Exchange server to a newer version by your Internet Service Provider (ISP) or company email server or IT administrator. After the Exchange upgrade, you can upgrade and reinstall the latest version of Outlook client for Windows 11/10.

Hope this post helps you!

Read: Connection to Microsoft Exchange is unavailable Outlook error

Why does Outlook say Unable to connect to proxy server?

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

• The connection to the server requires a certification authority (CA).
• You haven’t trusted the certification authority at the root.
• The certificate may be invalid or revoked.

What does proxy email mean?

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