The confUBINGRP macro determines the group ownership of user-executable files. This macro assigns its value to the BINGRP= Makefile directive, but only for the following programs: editmap, mailstats, makemap, praliases, rmail, vacation, and smrsh. This macro is usually correctly defined for you in your devtools/OS file. To change the group for these programs, you might do this:

define(`confUBINGRP', `users')

Note that the newaliases, mailq, hoststat, and purgestat programs are really symbolic links, so the concept of group does not apply.