break each ruleset into identified sections. (called groups).
note which groups can be reordered.
each group accepts and returns the same strings,
as much as possible.
reactivate Paul Vixie's RBL (in check_mail)
add rules to limit mail relaying to a list of hosts and domains
in the R class (check_rcpt, not active on hub.freebsd.org)
Submitted by: jmb
0bb6bbdc02