Am 26.03.2015 um 16:19 schrieb Kevin A. McGrail:
On 3/26/2015 11:11 AM, Robert Schetterer wrote:what he describes is not backscatter, cause the mail is rejected during smtp imcome stage, wich means the server simply didnt take the mail during the running smtp session,This argument to me assumes that their isn't a server in the middle of the relay. Not everything is edge to edge, point A to B. Lots of backscatter comes from attacking secondary MX's and
well, in case it is not edge-to-edge (backup MX and so on) you need to make sure that the backup MX has the same filter quality as the primary and in any case use a different port without restricitions for deliver that mails to the primary later
to say it short: the whole mail environment needs to be desigend from the start to a) reject a message or b) after answer with 2xx deliver it to minimize backscatters *and* provide reliable mailflow
just because you 5xx doesn't mean it doesn't cause backscatter
only if the sending environment is configured wrong, but in any case *you* are not triggering the backscatter and if we argue that way we also would need to stop using RBL's which rejects a majority of all incoming spam
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