Neil Schemenauer email@example.com writes:
I bring this up because "STMP time filtering" makes a bypass mechanism work much better. With a system like TMDA, confirmation notices usually generate double-bounces. Instead, we could reject the message with a 5xx error that includes instructions on how to bypass the filter (e.g. include a cookie in the body of the message).
TMDA doesn't do this because it would make more work for the sender to get his message delivered. Because TMDA stores the incoming messages in a local queue, the sender just has to reply to a confirmation request, and his original message gets delivered. As opposed to having to cut and paste his message from the body of a bounce and then resend it. So, not operating at the transport level saves your correspondents some work at the expense of some bandwidth.