Solution to the issue of an Unknown error from Messaging Interface

How to resolve the issue indicated by the message 'the messaging interface has returned an unknown error' in MS Outlook PST?

Outlook's Personal Storage Table (PST) files can be susceptible to multiple forms of corruption caused by both internal and external factors. One typical indicator of PST corruption in Outlook is the occurrence of an error message stating, 'the messaging interface has encountered an unknown error. If the issue persists, please restart Outlook.' These error messages may surface when performing tasks such as checking emails, sending faxes, creating new calendar entries, or deleting emails, calendar events, or contacts. How can you effectively address these situations?

Firstly, follow the message's advice and initiate a restart of Outlook to verify if the issue persists. In the event that Microsoft Outlook continues to exhibit abnormal behavior, consider implementing the following sequential solutions to address the corruption affecting MS Outlook PST files (applicable to versions 8.03 to 97): Utilize the Inbox Repair Tool, Create a New PST File, Establish a Fresh Outlook Profile, Install a New Set of MAPI Files, or as a last resort, consider reinstalling the Windows operating system. For a streamlined approach to mending corrupt PST files, explore the convenience of employing a specialized PST file repair tool like Kernel for Outlook Repair.

Method 1- Use Inbox Repair Tool (scanpst.exe)
The Inbox Repair Tool is a built-in Microsoft utility designed to address PST file corruption issues. You can utilize it as follows:
  • Exit Outlook completely, go to Start > Settings and click Control Panel.
  • Double-click Mail, go to Services tab, click Personal Folders, click Properties, note the path to the Personal Folder from the Path box and click OK.
  • Again go to Start, and point to Programs > Accessories > System Tools and click the Inbox Repair Tool.
  • Type the path to the Personal Folders (noted in the stpe2) in the Drives box and click Start to start the scan.
  • After the scan is complete, click 'OK,' and then restart Outlook to verify if the items are now accessible.
Method 2- Create New PST File

Creation of a new PST file involves creating a new PST file and importing the information from the original PST.

  • Exit Outlook completely, go to Start > Settings and click Control Panel.
  • Double-click Mail, go to Services tab, click Personal Folders, and click Remove.
  • Click Add, go to Available information services box, click Personal Folders and click OK.
  • Type the user's first name in the File name box, click Open, click OK twice and exit Control Panel.
  • Start Outlook, start working as usual and check if the issue is resolved. If the issue has been resolved, you can import the information from the original PST files by continuing with the steps given below.
To Import Information from the Original PST
  • Go to File menu and click Import and Export.
  • Click Import from a personal folder file (.pst) in the Choose an action to perform box and click Next.
  • Type the path to the PST file in the File to import box and click Next.
  • Ensure that Personal Folders is selected (as the folder to import from and the folder to import into) and click Finish.
Method 3- Create a New Outlook Profile

Exit Outlook completely, go to Start > Settings and click Control Panel.

  • Double-click Mail, click Show Profiles and click Add.
  • Select the services you need and click Next.
  • Provide necessary information related to the selected services on Inbox Setup Wizard.
  • Type new and click Next, when prompted to enter the path to PST files, and complete the steps in Inbox Setup Wizard.
  • Go to the General tab, go the When starting Microsoft Windows Messaging, use this profile box, select the newly created profile and click Close.
  • Open Outlook and start working as usual.
Method 4- Install a New Set of MAPI files

The Messaging Application Programming Interface (MAPI) for Outlook, often referred to as MAPI, serves as an API that developers can integrate into their applications. It empowers developers to create emails, store them, facilitate email notifications, and implement various related functionalities. To utilize the MAPI subsystem, it's essential to have a messaging application like Microsoft Outlook installed on your machine as a mandatory prerequisite.

MAPI library files are stored in the supported versions of Windows system under the path :




The information related to MAPI installation can be found in the registry editor under below path:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows Messaging Subsystem.

  1. To fix the Outlook crash issue, you need to first close all messaging applications or email applications such as Outlook.
  2. Then you need to goto the registry editor path - HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows Messaging Subsystem.
  3. Now export and then delete the existing file under this folder Next, move the mapi32.dll file to another location from the existing location.




  4. Visit the official Microsoft website to download the latest version of the 'mapi32.dll' file that is compatible with your specific Outlook version. After downloading, paste this file into the location mentioned in the previous step.
  5. Now restart your Windows and then open Outlook.
Method 5- Reinstall Windows

If all these methods fail, it is essential to reinstall the Windows in the system.

Method 6- Kernel for Outlook PST

To effectively mend corrupted PST files, consider employing a trustworthy PST file repair tool known as Kernel for Outlook PST Repair. This user-friendly tool is compatible with all versions of MS Outlook, making it a versatile choice. It simplifies the PST file repair process, ensuring a swift resolution without requiring extensive technical expertise. Kernel for Outlook PST Repair is renowned among Outlook users for its ease of use and is available in a demo version for evaluation. Once you've successfully repaired the corrupt or inaccessible PST file, you can resume your regular Outlook activities without any disruptions.