DCC - Postfix MTA mail hub implementation question

Tim Wicinski tim@meer.net
Fri Aug 23 21:18:21 UTC 2002

------ Paul Vixie, <20020823201126.C875D28B6C@as.vix.com> writes: 

    > One benchmark to look at may be virus checkers. Many of them offer to 
    > act as pseudo SMTP servers -- either in front of the real MTA or behind 
    > it in a filtering step in the SMTP chain. This is an example of a class 
    > of application with needs similar to DCC that has failed to foster a 
    > universal content filtering protocol (beyond SMTP itself).
    if you're rejecting e-mail at the MTA level because it is invalid or
    unwanted, then such rejection must be done synchronously (before the
    final 250) or else you're stuck with unbouncable garbage and you've put
    no disincentive on the sender to puke more of it in your direction.

We have that problem now with the MX servers feeding our IMAP/POP
servers.  If something passes step 1 but fails 2 (user unknown being
primary reason), the garbage most likely will sit on the MX machines
trying to be returned. 

You do want to do the DCC check synchronously. It defeats part of the
purpose to accept a message, then parse and reject it.  


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