LEAP 15.1 Which user delivers mail locally that arrives via Postfix

I am using emails delivered locally to trigger commands via the /etc/aliases file i.e. piping to a command. All works well until I want to run a command that requires root privileges. I use sudo but can’t work out which user is executing the command and so currently have:



in my /etc/sudoers file but want to lock it down by replacing the first ALL with the correct user. So for tried “mail” and “postfix”. Neither work. what should it be?

Thanks

PS Yes, I will be licking down the commands too, to just what I need