Sometimes the downstream MX has a 'special cookbook' of super secret anti-spam body checks, and you will always have this problem.
Vasya Pupkin wrote (on Thu, Jul 22, 2010 at 06:37:26PM +0400): > It is already as restrictive as possible and acceptable for me. I do > not want to loose any non-spam mail as well, so I am not going insane > adding network block based rbl domains, but I am using most reliable > rbl domains, including zen.spamhaus.org, bl.spamcop.net, > cbl.abuseat.org, b.barracudacentral.org, and some more, and some > Postfix internal check including reject_non_fqdn_sender, > reject_non_fqdn_recipient, reject_unknown_sender_domain, and some > more. > > On Thu, Jul 22, 2010 at 6:28 PM, Mikael Bak <mik...@t-online.hu> wrote: > > Vasya Pupkin wrote: > >> 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? > > > > Hi Vasya, > > > > To be sure to not acting as a backscatter you will have to configure the > > front mx to be as restrictive regarding content and mail sizes as the > > final destination is. Otherwise you will see problems like the theese. > > > > HTH, > > Mikael > > > > -- _________________________________________ Nachman Yaakov Ziskind, FSPA, LLM aw...@ziskind.us Attorney and Counselor-at-Law http://ziskind.us Economic Group Pension Services http://egps.com Actuaries and Employee Benefit Consultants
