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Backup Mailserver -Secondary MX server

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  • John Hinton
    My goal is to have a Postfix mailserver set up to accept mail for other Postfix servers running multiple domains if and only if they are not accessible . I
    Message 1 of 2 , Apr 1, 2013
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      My goal is to have a Postfix mailserver set up to accept mail for other
      Postfix servers running multiple domains 'if and only if they are not
      accessible'. I have been using Sendmail with milter-ahead set to:

      "+backup-mx
      For a backup MX or gateway, accept mail when the down stream mail
      server is unreachable or when the server returns 421 server busy or 554
      no service responses."

      This provides a catchall system if and only if a primary server is not
      accessible, thus eliminating the spam sent intentionally to the backup
      system. Over the years this has worked great.

      My searches are finding bad advice and not much in the way of this
      particular need. (I remember having the same problem years ago when
      trying to find something for Sendmail). It seems that the term backup is
      a bit too broad a meaning for this purpose.

      Anyway, if anyone has some good advice on what to use or where to start
      reading, I would appreciate it.

      And yes, sorry for the subject line yet again... It seems that secondary
      MX server might be a better description?

      --
      John Hinton
      877-777-1407 ext 502
      http://www.ew3d.com
      Comprehensive Online Solutions
    • Wietse Venema
      ... What s missing from this picture that not only hosts can fail, but also networks. Network outages happen all the time in different parts of the Internet.
      Message 2 of 2 , Apr 2, 2013
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        John Hinton:
        > My goal is to have a Postfix mailserver set up to accept mail for other
        > Postfix servers running multiple domains 'if and only if they are not
        > accessible'.

        What's missing from this picture that not only hosts can fail, but
        also networks. Network outages happen all the time in different
        parts of the Internet.

        As the result of outages in intermediate networks, the primary MX
        server will be reachable for most clients but unreachable for others.
        Therefore, the secondary MX server will see legitimate connections
        while the primary MX server is up.

        Secondary MX servers are a source of accept-then-bounce spam when
        they don't reject mail with "recipient unknown", and when they don't
        enforce the same anti-spam policy as the primary MXen. Such servers
        may eventually become blacklisted.

        Search the web for backscatter, outscatter, etc.

        Wietse
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