Hello list, I am trying to configure Postfix to process inbound mail in the following manner:
1. A sender connect to Postfix smtpd to deliver a message. 2. Postfix calls Milters A, B, C. Each of these Milters can either (a) reject the message, (b) accept the message without changes or (c) add a new header "X-SomeHeader: SomeValue" and then accept the message. 3. If any of the milters rejects the message (case 2a) Postfix rejects the delivery attempt in progress with code 5xx. 4. In case 2b (all milters accept without changes) Postfix signals 250 to the sender, terminates the inbound connection, looks up a "next hop" transport and passes the message to that destination. The tricky part is case 2c. Messages marked with one or more additional Headers, and only these messages, need to be passed to a fourth milter D after a delay (!) of somewhere between 90s and 5m (current estimate). Milter D then either accepts the message as is or adds yet another new header before accepting. As calling milter D depends on the presence and content of headers, I assume that it might be difficult to achieve the desired behaviour with built-in Postfix features of a single Postfix instance. I am currently exploring the idea of writing a transport service which FIFO-queues all inbound messages for case 2c, delaying them for X seconds before passing them to a second Postfix instance which talks to milter D. However, I'd rather use Postfix's own robust mechanisms (perhaps the deferred queue?) instead of implementing a queing transport from scratch. Also, I estimate that whatever queue I use will grow to hold approx. 1-5 million messages at peak times, so performance and robustness are key. If you have ideas that could help me solve this, I'd appreciate you letting me know. -Ralph
