While a PBS job is active, it's stdout and stderr streams are saved in a file on the MOM's node. These two files are in /tmp/pbs/working/spool. When the job completes, the MOM copies the files into the directory from which the PBS job was submitted.
If the directory pathname prefix is listed in a usecp command in the MOM's config file, the MOM will use cp to move the files over. If the pathname is not listed in a usecp command, the MOM will use a PBS remote copy command called pbs_rcp. It is preferable to use cp, since there are many reasons why a pbs_rcp command may fail. For this reason, all file systems that host users directories and that are mounted on all service nodes should be listed in the MOM's config file. (The config file is located in /tmp/pbs/working/mom_priv and is described in the our PBS README file.)
If for some reason the MOM can not copy over the output files, it copies them instead to the directory /tmp/pbs/working/undelivered. You can recover these and send them to the user.