The messaging interface returned an unknown error

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?

Personal Storage Table (PST) files of Outlook repeatedly may fall victim to many types of corruption due to various internal and external factors. A common symptom of Outlook PST corruption is the display of an error message of the type "the messaging interface has returned an unknown error. If the problem persists restart Outlook." You may receive such messages while trying to check emails, sending faxes, creating a new calendar item and deleting emails, calendar items or contacts. How can you deal with such situations?

Before attempting anything else, restart the Outlook as instructed in the message and check if the problem is still there. If MS Outlook does not work as usual, try the following solutions one after the other to resolve the corruption that is haunting the MS Outlook PST (versions 8.03 to 97): Use Inbox Repair Tool, Create New PST File, Create a New Outlook Profile, Install a New Set of MAPI Files, Reinstall Windows. You can repair the corrupt PST files more easily by using a PST file repair tool like Kernel for Outlook Repair.

Method 1- Use Inbox Repair Tool (scanpst.exe)

Inbox Repair Tool is an inbuilt Microsoft Tool to deal with the PST corruption issues. It can be used as below:

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.
Click OK when the scan is complete, and start Outlook again to check if the items are 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

Messaging Application Programming Interface for Outlook, commonly known as MAPI is an API for developers to use in their applications to create emails, store those emails, enable notifications for emails and various such features. MAPI subsystem requires a messaging application such as Microsoft Outlook to be installed on your machine as a prerequisite.

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

>drive>/Windows/System32/mapi32.dll

>drive>/Windows/syswow64/mapi32.dll.

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows Messaging Subsystem.

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

>drive>/Windows/System32/mapi32.dll

>drive>/Windows/syswow64/mapi32.dll.

Goto microsoft website and download latest mapi32.dll file compatible with your Outlook version and paste it in the location in the above step.
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

In order to repair corrupt PST files, you can use a reliable PST file repair tool named, Kernel for Outlook PST Repair. It is an easy-to-use tool that works with all versions of MS Outlook. The tool facilitates the quick repair of PST files without any technical complications. It is known among the Outlook users as the most user-friendly tool and is available as demo version. After repairing the corrupt or inaccessible PST, you can perform all Outlook activities as usual.