As I understand it the problem addressed is email that appears to come from one's own domain. Don't waste your time on this one. It is virtually and technically impossible to stop with ANY MTA in the world. Why? In SMTP mail there are actually two "from" headers. There is the "real from" header that can be keyed on by firewalls and MTA's and certainly something could be done here. But there is also a "display from" header which can be imbedded in the data portion of the email. The "display from" can be set to your own local domain and no firewall or MTA in existence is going to be able to detect it. The "display from" as well as the "display to" features of SMTP are well intentioned features that spammers have taken full advantage of. For example, suppose a CEO of a large company charges the secretary to send out an email to all employees. We want the "to" to simply display something like "To All Employees" instead of a list of thousands of individual email addresses. And we want the from to have the effect of the CEO's name instead of the secretary's name. You will never achieve 100% what you are after, not with postfix or any other MTA. The "display from" is a feature. You'll have to live with it.
