Navigate to the following registry key based on your Outlook version:
Outlook 2016 – HKEY_CURRENT_USER \ Software \ Microsoft \ Office \ 16.0 \ Outlook \ Preferences
Outlook 2013 – HKEY_CURRENT_USER \ Software \ Microsoft \ Office \ 15.0 \ Outlook \ Preferences
Outlook 2010 – HKEY_CURRENT_USER \ Software \ Microsoft \ Office \ 14.0 \ Outlook \ Preferences
Outlook 2007 – HKEY_CURRENT_USER \ Software \ Microsoft \ Office \ 12.0 \ Outlook \ Preferences
Right-click on Preferences, then go to New > Dword (32 bit) Value
Name the new Dword “DisableTNEF” and hit Enter to save
Double-click on DisableTNEF. Set the Base to Hexadecimal, then insert the value 1 in the box under Value data. Hit Ok and close the Registry Editor.