IMO this looks overly complicated, especially as SPF works fine. The only problem with SPF right now is that many receivers (including) GMail don't abide to the

IMO this looks overly complicated, especially as SPF works fine. The only problem with SPF right now is that many receivers (including) GMail don't abide to the specification. If there's an "-all" clause at the end this implies that you must not accept mails from other mail servers than the ones allowed. If you still do - your fault - but don't complain that your users receive mails with faked sender addresses.