I'm doing best I can to fight spam. What I described happens with spam that pierced through all filters. There is no 100% way to detect spam and you know that. So, some percentage will still go through and will be forwarded, and possibly rejected, causing bounce to be generated.
On Thu, Jul 22, 2010 at 6:27 PM, Wietse Venema <wie...@porcupine.org> wrote: > Vasya Pupkin: >> Hello. >> >> First, I have spent two days reading articles and searching web for >> solution but failed there. I am using postfix as an mx for my domains, >> it accpets mail for different addresses withing my domains which is >> then forwarded to other external domains, i.e. google.com and other >> mail services. Mail for unknown users is rejected, many other check >> are performed, but still sometimes my system acts as a backscatterer >> when something like this happens: >> >> 1. Incoming mail passes all tests, it's coming to one of the addresses >> within my domain, i.e. existing-u...@mydomain.tld >> 2. Postfix then forwards mail to external domain, i.e. >> myem...@mailservice.tld >> 3. For some reason mailservice.tld rejects this mail, i.e. it doesn't >> like it's content or size. >> 4. Postfix then bounces mail to sender, which can be forged, and thus, >> becoming a backscatterer. >> >> Is there any way to prevent postfix from sending bounces anywhere? > > The best conutermeasure is not to forward spam. > > The second-best solution requires the ability to predict if a > specific message will be rejected down-stream. Let me know when > you solve that, so I can add it to Postfix. > > Wietse >
