In order to add any program to startup when Windows starts simply copy the Shortcut to the Startup Folder
Open the command window (Win+R) and enter
%AppData%\Microsoft\Windows\Start Menu\Programs\Startup
This will open the Startup location in the File Explorer. Next from the Start Menu right click the program you want to have startup (Outlook in this case) and select More->Open File Location this will open the location of the program Shortcut. Finally copy and paste the shortcut into the Startup Folder.
Copied from Microsoft’s article here