How do you get Postfix to keep a log of all outgoing mails, in their complete form (all headers + payload) as received from clients? The closest param I've found so far is
always_bcc, but this loses some information (at least the RCPT-TO info). Thanks in advance for any hints.
You can use a content filter that stores a copy of the mail somewhere. There is pretty good documentation on it at http://www.postfix.org/FILTER_README.html. It also contains an example content filter script that does exactly what you want.