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?
