Add Readme file adn comments for/in postfwd2 resources.

install_postfix_advanced.sh

@@ -1200,6 +1200,36 @@ if [[ ! -f "/etc/postfix/postfwd.cf" ]]; then
 
 #======= Rule Sets ============
 
+# ---
+#
+# Processing of the Rule Sets
+#
+# The parser checks the elements of a policy delegation request against the postfwd set
+# of rules and, if necessary, triggers the configured action (action=). Similar to a
+# classic firewall, a rule is considered true if every element of the set of rules (or
+# one from every element list) applies to the comparison. I.e. the following rule:
+#
+#    client_address=1.1.1.1, 1.1.1.2; client_name==unknown; action=REJECT
+#
+# triggers a REJECT if the
+#
+#    Client address is equal (1.1.1.1 OR 1.1.1.2) AND the client name 'unknown'
+#
+#
+# Note:
+#    If an element occurs more than once, an element list is formed:
+#
+# The following rule set is equivalent to the above:
+#
+#    client_address=1.1.1.1; client_address=1.1.1.2; client_name==unknown; action=REJECT
+#
+#
+# triggers a REJECT if (as above) the
+#
+#    Client address (1.1.1.1 OR 1.1.1.2) AND the client name 'unknown'
+#
+# ---
+
 # Whitelists
 
 # Whitelist trusted networks