When sending files through a series of machines, the intermediary machines must have the command uucp among their COMMANDS options. If you type the following command, the forwarding operation works only if machine willow permits machine oak to execute the uucp program.
% uucp sample.txt oak\!willow\!pine\!/usr/spool/uucppublic
The machine oak also must permit your machine to execute the uucp program. The machine pine, as the last machine designated, does not have to permit the uucp command because the machine is not doing any forwarding operations. Machines are not normally set up this way.