backup MX & Misdirected bounces

[Marek Barton]

Zdravim,

resim problem, jak spravne zkonfigurovat sendmaila, aby neposilal DSN 
zpravy spameru. Problem vznika tak, ze spamer posle zpravu, jako odesilate 
uvede nekoho, komu chce spam poslat a posle to na neexistujici adresu na 
mem serveru. Pokud se jedna o domenu, ktera je lokalni na mem serveru, tak 
spravne jeste behem relace zjistim, ze uzivatel neexistuje a zprava se 
odmitne a negeneruji zadny bounce, ktery by odesel na adresu v hlavicce 
from.
Problem je v tom, ze muj server dela take zalozni MX pro spousty 
domen, o kterych samozrejme nevi, zda konkretni maily existuji ci nikoliv. 
Prijme tedy dany mail do spoolu, snazi se ho dorucit na primarni MX 
server, jenze ten mu behem relace rekne, ze mail neexistuje, a tak muj 
server vygeneruje bounce, ktery odesle na podvrzenou adresu z hlavicky 
from nic netusicimu uzivateli, ktery ten spam vubec negeneroval.

Ve FAQ SpamCopu k tomu pisi toto:

Problem: Misdirected bounces
     Description: When a mail server accepts a message and later decides 
that it can't deliver the message, it is required to send back a bounce 
email to the sender of the original message. These bounce emails are often 
misdirected.

     Solution: Upgrade and/or configure your mail server software so that 
this situation is never encountered. Configure your software to either 
reject messages during delivery or accept them permanently. Do not let 
your software make choices about delivery after it has accepted a message. 
If you must accept delivery before you know the status of a message, then 
file it internally - do not send, forward or bounce it outside your 
organization. The errant message can be placed in a special folder or 
routed to your postmaster.

- cili mi radi, ze pokud uz ten mail prijmu do spoolu, aniz bych vedel, 
zda mail dorucim ci nikoliv, tak at pak neodesilam zadny bounce smerovany 
mimo server.

Pominu tedy moznost, kdy se nebude jednat o spam, primarni MX bude 
skutecne dole, ja prijmu regulerni mail do meho zalozniho spoolu od 
nekoho, kdo se pouze uklep v adrese a pri dorucovani mailu na primarni MX 
nevygeneruji bounce o neplatne adrese, cili odesilatel se nikdy nedozvi, 
ze jeho mail nedosel.

Jak se tedy sendmail nakonfiguruje tak, aby bouce posilal pouze lokalnim 
uzivatelum? V dokumentaci jsem to bohuzel nenasel.

dekuji

Marek Barton