* Marc Roos: > 3. system recognizes as this email never been seen before > 4. auto reply with something like (maybe with a wait time of x hours): > Your message did not receive the final recipient. You are sending > from a known spam provider
Generating backscatter is definitely not a good move, and it is even prone to punish yourself. Better to reject the offending message with a 5xx status code and some explanatory text or the URL. The various tests required to come to a decision about accepting or rejecting the message can be executed in a milter. Milter-regex, for example, is lightweight but still powerful enough to perform tests on combinations of various headers and the body content. Beyond that, a custom milter is always an option. -Ralph
