rtrfilter can be used to filter rancid diffs to avoid sending unwanted
diffs to certain recipient(s) or diffs which those recipient(s) should
not see without the need to create a separate group(s).

/etc/aliases eg:

rancid-foo:	engineering,
		customer-ops-foo
#
# only send diffs for the SJC routers (aka. *.sjc.shrubbery.net)
customer-ops-foo:	"| /home/rancid/util/rtrfilter -i '\.sjc\.' -s 'sjc router diffs' customer-ops"
#
customer-ops:	jimbob,
		sally