Support: Windows 7+
Registry path: HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\Outlook\Security\PromptSimpleMapiSend
Available values:
0
: Automatically deny1
: Prompt user (Default)2
: Automatically approve
Drawbacks:
If set to 2 (Automatically approve) it will allow any program to send emails through MAPI without any user interaction. I wouldn't suggest to apply this value unless strictly necessary.