How do I configure the mail server to work with GoodCrypto and other filters?

GoodCrypto's filter should be the first filter for inbound mail and the last filter for outbound mail.

If you want other content filters to run (e.g., an antivirus filter), then we recommend you either follow Wietse Venema's (the author of postfix) advise configure a separate instance of postfix for each filter or use a third party product like Amavisd-new.