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240647Re: backupmx with Postfix

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  • mouss
    Jul 1, 2008
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      Nicolas Letellier wrote:
      > On Tue, 01 Jul 2008 11:04:53 +0200
      > mouss <mouss@...> wrote:
      >
      >> If you have relay_recipient_maps set, then postfix will _reject_, not
      >> bounce. it is the "previous" MTA that generates the bounce. This is why
      >> you should reject on the first server that you manage and let others
      >> bounce or do whatever they want.
      >>
      > But, if Postfix rejects a mail, it sends a mail to inform that the mail has been rejected or not?
      > If rejecting a mail, Postfix send it to /dev/null and do not send any mails to sender, it's a good news!
      >
      >
      >

      do not confuse "reject" and "bounce".

      here is a reject example: C is a remote client (MTA or other). S is your
      server.

      C->S: connect
      S->C: show greeting banner
      C->S: says helo
      S->C: show supported extensions (auth, tls, ... etc)
      C->S: MAIL FROM: <sender@...>
      S->C: OK
      C->S: RCPT TO: <invalid@...>
      S->C: rejected. recipient does not exist
      C->S: QUIT

      no message is exchanged here. your server does nothing after this. it
      does not send a bounce. If C is a normal MTA, it is its responsibility
      to generate a bounce, but this none of our business: we don't care.

      If on the other hand your server is misconfigured, it will accept the
      mail during the smtp transaction. then later it will find out that it
      cannot deliver the message. it will then generate a bounce and send it
      to the original sender. sometime ago, this was ok, but since a lot of
      spam uses forged addresses, such bounces go to innocent people who did
      not send anything. This is backscatter.
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