Les Mikesell wrote:
The point here is that it is up to the sender to retry. If you tempfail the first attempt you have no control over how long it will be until the next attempt happens. If the sender has a big queue, it could be 4 hours or more.
That *could* happen. In practice, I've not seen it. In any event, it would happen only once for a given sending MTA. If that is the price I have to pay for reducing incoming SPAM by over 80% it is well worth it. In a short period of time all of those MTA's will long delays will be cached.
I bet those people that fret over this also have their user agents set to poll for new mail every minute.
At the very least you should permit a sending host once it is known to retry. Some schemes match up senders/recipients - which is appropriate for the first connection, but once you know a host is going to retry you might as well let it through.
That is what the cache does....without any human intervention.