Solved: The Outlook Is Unable To Connect The Proxy Server Error


An Outlook user goes through a number of Outlook errors. Few of them are simple to understand and few are complex. One such complex issue is related to an Exchange server’s error “The Outlook is unable to connect the proxy server”. The article provides a brief insight into the exchange proxy server and the causes that are responsible for the error. By the end of this reading, you will be able to understand and fix the error The Outlook is unable to connect the proxy server.


The error: Outlook unable to connect to the proxy server

We all know that Outlook is the most widely used email application over any other application. Not only as an email client, but Outlook also offers many other added benefits such as calendar, task manager, contact manager, note-taking, journal, and etc. Despite all the popularity that Outlook holds, it’s too vulnerable for errors

About Outlook Exchange Proxy Server: Why it is unable to connect?

Exchange Server:

An Outlook exchange server uses the Mailbox server role ( a multi-role server) for sending outbound emails through a send connector. Send Connector allows you to send emails from your Exchange server to other domains out on the Internet. When you click on the properties of Exchange’s send connector, you would find an option to proxy through a client access server.

A Proxy Server:

A proxy server is a network from where all your client’s queries or requests are sent to the main server. Basically, a proxy server acts as an intermediate network to send and receive the request sent by the clients to the server and vice versa. The error: Outlook is unable to connect the proxy server is related to a security certificate of the proxy server. 

A Security Certificate:

A security certificate is used to authenticate your MS Exchange server to communicate only with the authenticated servers. When Microsoft Outlook tries to connect to a server by using a remote procedure call (RPC) connection or a secure HTTP (HTTPS) connection, you receive one of the following error messages:

    • 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. The outlook is unable to connect to this server (Error code 10).
    • There is a problem with the proxy server’s security certificate. Outlook anywhere is unable to connect to the proxy server (Error code 10).
    • There is a problem with the proxy server’s security certificate. The security certificate is not from a trusted certifying authority. The outlook is unable to connect to this server (Error code 10).

To look further, let us go through the reasons that are responsible for the error to occur:

Why Does Outlook Say Unable to Connect To Proxy Server?

Listed are the few of the major reasons that cause the error “The outlook is unable to connect to this server”

  • When you try to connect to the server and the connection requires a certification authority.
  • Unable to make use of certification authority at the root
  • The certificate may be invalid or denied
  • The name of the site does not match the name in the certificate
  • A third-party add-in or a third-party browser add-in is preventing access or sometimes due to corruption in the Outlook file.

How Do I Fix the Proxy Server Security Certificate In Outlook?

Below mentioned are a few ways to fix Outlook unable to connect to Proxy Server error:

Verify the certificate:

In case of the invalid certificate name or Outlook is failing to connect with the proxy server, two things should be verified thoroughly. First, the expiry date of the certificate and next, the information mentioned in the subject field must match the name of the site. 

Follow the steps below to examine the certificate:

  1. Open internet explorer and connect to any secure and trustworthy server and press Enter key. Or type https://www.[servername].com/rpc” in the address bar of the browser and after that, hit the Enter key. Then, Connect with the RPC Server.
  2. Once you can find the padlock icon in the lower-right corner of the web browser, double-click on it and select the Details tab.
  3. Note the information from Valid to and Subject fields.

If the date is accurate as per the information given in detail and the subject matches the site name, then your certificate is up to date. If not, it’s expired or you need to make changes to the site name.

Install the trusted certificate:

If you encountered an error notification stating that the security certificate is not from a trusted authority or it is not added in Microsoft  Management Console (MMC, that holds all the certificate snap-ins). 

Following are the steps to install the trusted root certificate:

  1. When the Certificate dialogue box opens, click on the Install Certificate option and Next to proceed.
  2. Check the box Place all certificates in the following store. 
  3. Now, click Browse to select the Trusted Root Certification Authorities and click on OK. Click on Next to proceed further.
  4. Wait for the process to complete. Once it is completed, click on the Finish button. 

If the error still persists and you are unable to get rid of the error, try adding the certificate snap-in to MMC.

  1. Open Run (Windows + R) and type mmc. Click Yes.
  2. Go to File > Add/Remove Snap-ins.
  3. Select Certificates, then choose Add.
  4. Click on My user account.
  5. Select Add again and this time select Computer Account.
  6. Move the new certificate from the Certificates-Current User > Trusted Root Certification Authorities into Certificates (Local Computer) > Trusted Root Certification Authorities.
Turn off third-party add-ins:

Third-party add-ins are responsible for most of the Outlook errors including proxy server error,  0x80040154 and others. If the error shows, the security certificate is invalid or does not match the name of the target site, follow the below-mentioned steps to accomplish the desired results:

  1. If Outlook is running in your system, close it and press the Win+R key to open the Run window.
  2. In the Run search bar type “outlook.exe /safe” and click on OK.
  3. If you can operate the safe mode without any issue, that means the problem is with the third-party add-ins.
  4. To disable third-party add-ins, go to the File option on the top of the Outlook screen.
  5. Select Options from the file menu and click on Add-ins.
  6. Locate the manage Box and click on the COM Add-ins.
  7. Click on Go to move further.
  8. Do you see the checkbox next to the third-party add-ins? Clear that.
  9. Restart Outlook.

If none of the above-mentioned solutions successfully worked for you, then the issue might be in the Outlook file. Your Outlook PST or OST might be corrupted due to some malware intrusion or any other reasons.

Outlook PST files are stored on network servers. When your PST file is on a server which is facing issues, your PST file might become inaccessible. Additionally, if the server breaks down it might even corrupt your PST file.

In such situations, you can make use of the SFWare Outlook repair tool to repair any corrupt Outlook file. There is no harm in trying all the possible solutions to make the application work. 

SFWare Outlook PST Repair tool is a specialized tool to fix any damage or corrupt Outlook data file. Built with features like Normal Scan and Smart Scan help in fixing the complex PST file issues easily. The tool works on read only mode, to ensure no harm is caused to generate a healthy PST file. Download the software now and fix the PST file corruption in few simple steps.

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As cited above in the article,  “Outlook is Not Able to connect to the proxy server” is an error related to the exchange server. With the help of the above-mentioned methods, you can try fixing the error and make your Outlook work without any hassle. If your Outlook file is corrupted, you can always rely on the SFWare Outlook repair tool for easy assistance.

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