[plug] Re: Mail blocking

[Luke Dudney]

Bret Busby wrote:

>On Thu, 13 Dec 2001, Luke Dudney wrote:
>
>>No, the REJECT on the RHS of the map means to reject the message with a 
>>"552 Error: content rejected"
>>The sending MTA should bounce the message back to the envelope sender.
>>
>>And it's the DENY target in ipchains that drops the packet silently.
>>
>
>Wouldn't it be more appropriate, to just silently drop the packet, so
>that the spammer can't trace the party blocking the message?
>
>Can DENY, or an equivalent command, be used in the postfix command line,
>to silently drop the packet?
>
Probably, but IMHO that's RFC breaking behaviour.
That reminds me of a quote from Wietse Venema, author of Postfix:
  - "Junk mail is war. RFCs do not apply."

Nonetheless,

RFC2821

6.1 Reliable Delivery and Replies by Email

   When the receiver-SMTP accepts a piece of mail (by sending a "250 OK"
   message in response to DATA), it is accepting responsibility for
   delivering or relaying the message.  It must take this responsibility
   seriously.  It MUST NOT lose the message for frivolous reasons, such
   as because the host later crashes or because of a predictable
   resource shortage.

   If there is a delivery failure after acceptance of a message, the
   receiver-SMTP MUST formulate and mail a notification message.


To accept the email and then silently drop it (ie. don't reject it and 
don't send a bounce) is clearly contradictory to this.
I believe sendmail has a DISCARD feature which will do what you want 
(jump in here sendmail gurus).
I don't think Postfix can do this easily.

Anyway, generating bounce messages, queueing them, and then delivering 
them will take up excess resources on the sending host, which is an 
extra incentive on the systems administrator to close their open relay 
(which is where a lot of spam will get to you via).
I don't know if most spammers even check the mailbox of the return-path 
they use. How many times have you replied to one of the yahoo.com (or 
whatever) addresses and got a "mailbox full" or "user unknown" error?

Cheers
Luke