How to Fix the “Outlook cannot connect to server” Error?

Summary: Outlook may fail to connect to the Exchange server due to several reasons. The error occurs when authentication between Outlook and Exchange server fails due to corrupt profile, damaged or inaccessible OST file, synchronization issues, etc. In this guide, we’ve mentioned the reasons behind the error and the solutions to fix the 'Outlook cannot connect to server' error.

How to Fix the “Outlook cannot connect to server” Error?

Outlook, when configured with Exchange server profile in Cached Exchange Mode, creates an OST or Offline Folder file. This OST file is encrypted with a unique MAPIEntryID GUID key, which is stored in the registry of your local system and Exchange server. Although Outlook OST file allows users to work even when the system is offline, it needs to authenticate the user profile by matching the MAPIEntryID GUID key with the server mailbox at least once to allow access to OST and Outlook profile.

However, when this authentication fails, Outlook cannot connect to the Exchange server mailbox and displays the following or similar error message.

Cannot start Microsoft Outlook. Cannot Open Outlook Window. The set of folders cannot be opened. The file C:\Users\….\ cannot be accessed. You must connect to Microsoft Exchange at least once before you can use your Outlook data file (.ost).

Cannot start outlook

Why Outlook is Not Connecting to Server?

Outlook may fail to connect to the Exchange server due to various reasons, such as:

  • Connectivity issues
  • OST synchronization errors
  • Damaged OST file
  • A deleted or disabled mailbox from the Exchange server
  • Damaged Microsoft Office or Outlook program files
  • Corrupt Outlook profile
  • Incompatible or faulty add-ins

Methods to Resolve Outlook Cannot Connect to Server Error

You can fix Outlook not connecting to server issues in Windows by following the given methods. These methods work on Outlook 2007, 2010, 2013, 2016, and 2019.

However, you should backup your OST file to a safer location before applying these methods. This will help prevent permanent data loss if these fixes do not work for you.

IMPORTANT NOTE: If your mailbox is disabled or deleted from the server, the following solutions will not work. In such a case, the OST file enters the orphaned stage and becomes inaccessible. However, you can convert such OST file to PST or export the OST file directly to a new or existing live Exchange mailbox or Office 365 account using Stellar Converter for OST . The tool can also help you restore missing or deleted mail items.

Method 1: Restart System and Check Internet Connection

A simple system restart can sometimes do magic! It can resolve issues with Windows and other applications. So begin by restarting your system. Then check the internet connection and start Outlook.

If you still see the same error message and Outlook cannot connect to the server, follow the next method.

Method 2: Disable Add-ins

Incompatible or faulty Outlook add-ins may prevent or disrupt Outlook connection with the Exchange server. To check if the error is caused by a faulty add-in, follow these steps:

  • Press Windows + R keys, type Outlook /safe, and press the Enter key or click ‘OK.’ This will open the Outlook in safe mode.
Outlook /safe mode
  • Click File > Options.
  • Click ‘Add-Ins‘ and then click the ‘Go…‘ button beside Manage: COM Add-Ins.
  • Uncheck all Add-Ins and then click ‘OK.’
Uncheck all Add-Ins
  • Restart Outlook in normal mode.

If the error is resolved, activate each add-in, one-at-a-time, and observe Outlook for the error. This will help you find and remove the faulty add-ins.

However, if the error still appears when you open Outlook, follow the next method.

Method 3: Create a New Outlook Profile

Outlook may fail to connect to the Exchange server due to authentication failure, if your profile gets damaged. In such a case, you can create a new Outlook profile to fix the error. The steps are as follows:

  • Open Control Panel and search ‘Mail.’ Then click on the ‘Mail’ option.
Open Control Panel and search Mail
  • Click ‘Show Profiles‘ and then click ‘Add….
show profiles
add new profile
  • Enter the Profile Name and click ‘OK.’
Enter the Profile Name
  • Configure your new profile with your email account and click ‘Finish.
Configure your new profile
  • This will create a new Outlook profile.

Now open Outlook, choose the new Outlook profile and configure it. Then check if you can access the Outlook and mailbox items from the OST file. If not, head to the next method.

Method 4: Reinstall Microsoft Office

Damaged or corrupt Microsoft Outlook or Office program files can also lead to connectivity errors. You can resolve this by repairing or reinstalling the MS Office program.

Steps to repair MS Office installation:

  • Open Control Panel and click Uninstall a program.
 Uninstall a program
  • Select Microsoft Office program and then click ‘Change.
Microsoft Office program
  • Select ‘Repair’ and then click ‘Continue’ to repair the MS Office.
repair MS Office

Now try opening MS Outlook. If this does not resolve Outlook cannot connect to server issue, you can try reinstalling the MS Office.

Steps to uninstall MS Office from the system and install it from scratch:

Office uninstall support tool
  • Click ‘Install.‘ After the installation, it will launch the ‘Microsoft Support and Recovery Assistant‘ utility.
Microsoft Support and Recovery Assistant
  • Click ‘I agree.’
I agree
  • Select the Office version you want to uninstall and click ‘Next.’
Select the Office version you want to uninstall
  • Follow the wizard to uninstall MS Office and then restart your system.
  • The tool will reopen automatically and finish the uninstall process.
  • Then select the MS Office version you want to install and follow the wizard.

You may also download the MS Office setup and install it manually. Then open the MS Outlook, configure your email profile, and check if your Outlook is now connecting to the Exchange server and working. If not, follow the next method.

Method 5: Rebuild or Recreate OST file

If the above solutions did not work for you, try recreating the Outlook data file, i.e., OST. You can do this by either deleting, moving, or renaming the current OST file. By default, the OST file is located at C:\Users\UserName\AppDataLocal\Microsoft\Outlook\. However, the OST file location may vary based on the Outlook version. For more details, check our guide to locate the OST file.

Once found, delete, move, or rename the file with the .old or .bak extension. Now open Outlook. If your profile and the mailbox on the server are still active, a new OST file will be created and mail items will be synchronized from the server.

backup ost file

But if the OST file is not recreated, it indicates a disabled or deleted mailbox or profile. In such a case, you can’t do much but convert the orphaned OST file to PST format using the OST to PST converter tool , as mentioned earlier. Then import the PST file into your new Outlook account.


The ‘Outlook cannot connect to server’ error may render your Outlook account useless and result in a data loss situation, if not resolved. The error prevents you from accessing the Outlook account and mailbox items as it fails to connect to the Exchange server.

We’ve discussed various methods in this post to troubleshoot the Outlook cannot connecting to the server error. However, if your profile is deleted or disabled from the server, these fixes won’t work. In such a case, you can convert the backup OST file to PST using Stellar Converter for OST. Then import the converted PST into your new Outlook or Exchange profile and restore your mail items. The software also provides options to import the mail items from orphaned or inaccessible OST directly into a live Exchange mailbox or Office 365 account.

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