Outlook 2021 (MSO) - Troubleshooting Email Sending via MAPI

This article aims to provide a comprehensive guide on troubleshooting email sending issues in Outlook 2021 (MSO) using MAPI (Messaging Application Programming Interface).

Outlook 2021 (MSO) Environment

The customer reports an issue where applications cannot send emails through Outlook 2021 (MSO), version 16.0.15731.20822, a 32-bit version of Office.

Prerequisites

Before proceeding with the troubleshooting steps, ensure the following:

• Your system meets the minimum requirements for Outlook 2021.
• Outlook is configured correctly.
• Your antivirus software is not blocking Outlook.

Step 1: Check Outlook Account Settings

Incorrect account settings can prevent emails from being sent via MAPI. Follow these steps to check your account settings:

1. Click on the "File" tab in Outlook.
2. Select "Info" and then click on "Account settings" at the bottom of the window.
3. In the "Account settings" dialog box, click on the email account that you're having trouble with.
4. Click on the "Change" button under the "Server information" tab.
5. Make sure that the incoming and outgoing mail server addresses are correct.

Step 2: Check MAPI Diagnostic Log

The MAPI diagnostic log can help you identify the root cause of the issue. To enable and view the MAPI diagnostic log:

1. Press "Windows key + R" to open the Run dialog box.
2. Type "regedit" and press Enter.
3. Navigate to the following registry key:
HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Profiles\\\Mapi

Replace and with your actual profile name and email address.

4. Right-click on the empty space in the right pane and select "New" > "DWORD (32-bit) Value."
5. Name the new value "DiagnosticLogLevel" and set its value to "1."
6. Close the registry editor.
7. Restart Outlook.
8. Try to send an email.
9. After sending the email, press "Windows key + R" to open the Run dialog box, type "notepad" and press Enter to open Notepad.
10. In Notepad, click on "File" > "Open" and navigate to:
%AppData%\Local\Microsoft\Outlook\\\Diagnostics\

Replace and with your actual profile name and email address.

11. Select the MAPI diagnostic log file (it will have a .txt extension) and open it in Notepad.
12. Look for any error messages related to the issue.

Step 3: Repair Outlook

If the issue persists, try repairing Outlook:

1. Click on the "Start" menu and select "Settings."
2. Click on "Apps" and then "Apps & features."
3. Find "Microsoft Office Desktop Applications" and click on "Advanced options."
4. Select "Outlook" and click on "Repair."
5. Follow the on-screen instructions to repair Outlook.

Step 4: Reinstall Outlook

If repairing Outlook doesn't work, try reinstalling it:

1. Click on the "Start" menu and select "Settings."
2. Click on "Apps" and then "Apps & features."
3. Find "Microsoft Office Desktop Applications" and click on "Modify."
4. Select "Outlook" and click on "Change."
5. Follow the on-screen instructions to uninstall Outlook.
6. Download and install the latest version of Office from the Microsoft website.

References

For further reading, refer to the following resources:

• Microsoft Support: Troubleshoot mail issues using the MAPI diagnostic tool
• Microsoft Docs: Troubleshoot email problems in Outlook