Two programs need to be executed as root no matter who runs them. One is sendmail (prior to V8.12), and the other is mail.local. Should one or both of these programs have to run as a user other than root, you can redefine the user with this confSBINOWN macro:

define(`confSBINOWN', `nullmail')

Note that this is just half of the solution. You will also need to tune the appropriate F=S delivery agent flag (see F=S for a description of how to do this).