Please check if the E-mail Converter add-in is disabled or inactive in Outlook.
Open the “File” tab and select “Options”.
An Outlook Options window will open. Click on “Add-ins”.
From the “Manage” dropdown select “Disabled Items” and click on “Go”.
Select E-mail Converter and click on “Enable”.
Open the “File” tab and select “Options”.
An Outlook Options window will open. Click on “Add-ins”.
Select E-mail Converter and click on “Go”.
Check the box E-mail Converter and click OK.