DCC - Postfix MTA mail hub implementation question

Paul Vixie wrote:

>>For postfix the dominant cost is not fork/exec but management of the 
>>queue files. The postfix content filtering scheme involves the mail 
>>totally leaving the postfix universe (it is effectively "delivered" to 
>>the content filter), so the queue file is deleted. [...]
>>
>there is no way under that model to reject the mail before the final-ok
>after the DATA/. verb, so that the mail stays with the spammer's mailer
>(or the open relay or whatever).  there has to be a way to do synchronous
>rejection.  attempting to bounce spam after accepting that DATA/. verb
>is just not worthwhile.
>
Yep, if you want to bounce at the SMTP level DCC has to be inserted into 
the smtp server or must interface with it with a protocol like Vernon 
described.