Outlook is Not Able to Connect to the Proxy Server, Find Solutions

As an Outlook user, we know that it can be configured with the Exchange Server and other accounts easily using Server and Client settings. Due to some disturbances in the Proxy Server (network to send client’s queries or requests to the main server), users have to encounter an error – “MS Outlook is not able to connect to the Proxy Server”.

This error issue more often occurs when there is faulty third-party Add-ins or issues with Security Certificate (for authenticating the MS Exchange Server to communicate with the authenticated Servers) such as invalid/cancelled certificate, mismatch between site and certificate name, certification authority at root is not possible, etc.

Fixing “MS Outlook is not able to Connect to the Proxy Server” Issue

Analyzing all the conditions and scenarios, we have concluded some fixes for your benefit. Try executing the processes one after another. If one process does not prove helpful, you can move on to the next process as the solution.

Try Disabling Third-Party Outlook Add-ins and Browser Add-ins

Faulty third-party Add-ins can be suspected as the culprits behind the Outlook connection issue with the Proxy Server


First run the Microsoft Outlook application by typing outlook /safe and click on OK in the Windows Run box.

“There is a problem with the proxy server’s security certificate. The name on the security certificate is invalid or does not match the name of the target site outlook.office365.com. Outlook is unable to connect to the proxy server (Error Code 0).”

Note: To open the Windows run box, press Windows and R alphabet together.

Now, the issue within Add-ins can be inferred if the Outlook application opens successfully in the safe mode. Here, you need to disable the Outlook Add-ins which you suspect to causing the issue. For that, perform these instructions.

  1. In the Outlook application opened in the safe mode, go to File>>Options.
  2. On the Outlook Options page, click on the Add-ins option from the left panel list and then move on to the right panel, from the Manage box, click on COM Add-ins option and then hit on Go option.
  3. From the Add-ins dialogue box, unselect the Add-ins which you want to disable and then click on OK.
  4. Now, exit the Outlook application in the safe mode and then restart it.

Users can disable the third-party browser Add-ons from Internet Explorer as Outlook application utilizes this browser’s settings for HTTP requests as the issue can occur also with the faulty browser Add-ons.

One can disable the Add-ons in Internet Explorer using these steps.

  1. Launch the Internet Explorer browser on your system.
  2. Go to the Tools menu and hit on Manage add-ons option.
  3. Go to the Show section, select all Add-ons and then disable each one of them using the Disable option.
  4. Click on Close and then restart the Internet Explorer to check if all is good.

Try Checking the Certificate for Error

Examining the security certificate causing the error is one of the top solutions which users can perform as a solution for these two error messages.

“There is a problem with the proxy server’s security certificate; %s. Outlook is unable to connect to this server. (%s).”

“There is a problem with the proxy server’s security certificate, %s. The name on the security certificate is invalid or does not match the name of the site. Outlook is unable to connect to this server. (%s).”


  1. In the Microsoft Internet Explorer, establish a connection between the secure RPC server using this URL –
    Provide the secure server or RPC server name in the above link.
  2. Now, go to the padlock icon in the opened page from the right most corner of the page and double-click on it. Click on the Details tab then.
  3. Under the Details section, check the Valid to and Subject field information like valid date, subject, etc. confirms with the provided site name. If the details are not matched, users need to change the server name.

Try Installing Trusted Root Certificate Error

Installing the trusted Root Certificate Error in case of the following proxy error is suggested.

“There is a problem with the proxy server’s security certificate, %s. The name on the security certificate is invalid or does not match the name of the site. Outlook is unable to connect to this server. (%s)”


  1. On your Exchange Server, go to the Certificate dialogue box then click on the Install Certificate option. Click on the Next to continue.
  2. Then select the checkbox saying “Place all certificate in the following store”.
  3. Select the Trusted Root Certificate Authorities by clicking the Browse option. Hit on Next.
  4. Let the installation process to get completed. When got completed, click on Finish option.
  5. Click OK.

The explained manual strategies are completely based on the type of error users receiving when Outlook fails to connect to the Proxy Server.

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We learned some beneficial solutions to get out of the situation where Outlook emails are not being received or delivered due to error “Outlook is not able to connect to the proxy server”. Additionally, the knowledge about an efficient PST Repair professional tool is provided to all.