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Re: Postscreen DNSBL Sites

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  • /dev/rob0
    ... Since you mention mjabl I think you might not be familiar with these DNSBL (and DNSWL) services. It bears repeating: you really should become familiar
    Message 1 of 67 , Apr 23, 2013
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      On Tue, Apr 23, 2013 at 08:59:41PM -0700, David Benfell wrote:
      > On 04/23/2013 10:42 AM, Steve Jenkins wrote:
      > >
      > > This setup has been working pretty well for me, and reduces false
      > > positives by not allowing any single DNSBL to block an incoming
      > > connection without concurrence from at least one other DNSBL.
      > >
      > First, thanks for introducing me to postscreen. Since I moved my
      > domains to a dedicated server in Germany, I've been getting
      > hammered with spam, so second, I've been testing this out, minus
      > the mjabl entry, and it seems to have stopped the spammers in their
      > tracks. I'm not going to claim it's optimum, because I don't know,
      > but it works *very* well.

      Since you mention "mjabl" I think you might not be familiar with
      these DNSBL (and DNSWL) services. It bears repeating: you really
      should become familiar with them.

      Did you sign up for Barracuda Reputation Block List? It's free of
      charge, but they do require registration.

      Links are on my page that you will see (or have seen) upthread. Take
      the time to know the policies of each of these services.

      Good luck, and enjoy watching the spam rejections. :)
      --
      http://rob0.nodns4.us/ -- system administration and consulting
      Offlist GMX mail is seen only if "/dev/rob0" is in the Subject:
    • Stan Hoeppner
      ... permits always come before rejects . Thus whitelist type entries should always be at the top of the restrictions list. As you are using
      Message 67 of 67 , May 14, 2013
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        On 5/14/2013 11:45 AM, Steve Jenkins wrote:
        > On Tue, May 14, 2013 at 8:33 AM, /dev/rob0 <rob0@...> wrote:
        >
        >> On Tue, May 14, 2013 at 07:49:50AM -0700, Steve Jenkins wrote:
        >>> smtpd_recipient_restrictions =
        >>> reject_invalid_helo_hostname,
        >>> warn_if_reject reject_non_fqdn_helo_hostname,
        >>> reject_unknown_reverse_client_hostname,
        >>> warn_if_reject reject_unknown_helo_hostname,
        >>> check_reverse_client_hostname_access
        >> pcre:/etc/postfix/fqrdns.pcre,
        >>> check_helo_access hash:/etc/postfix/helo_access,
        >>> check_sender_access hash:/etc/postfix/sender_access,
        >>> reject_rbl_client zen.spamhaus.org,
        >>> reject_rhsbl_client dbl.spamhaus.org,
        >>> reject_rhsbl_sender dbl.spamhaus.org,
        >>> reject_rhsbl_helo dbl.spamhaus.org,
        >>> permit_dnswl_client list.dnswl.org=127.0.[0..255].[1..3],
        >>> permit
        >>
        >> The last two lines are no-op. If you have anything you want to be
        >> subjected to the list.dnswl.org whitelist, put it after the
        >> permit_dnswl_client. If not, there is no point in querying it.
        >
        >
        > Excellent point. If the next step is going to "permit" anyway, then no use
        > in the extra query. I've moved the dnswl.org line up so that it's just
        > above the three "local" check_* lines.

        "permits" always come before "rejects". Thus whitelist type entries
        should always be at the top of the restrictions list. As you are using
        (client|helo|sender|recipient) sections any whitelisting in
        smtpd_recipient_restrictions should typically be at the very top.

        permit_dnswl_client list.dnswl.org=127.0.[0..255].[1..3]
        ^^^^^^ ^^^^

        This shows you are explicitly permitting anything/everything listed in
        the dnswl. Are you sure that is what you want? I use...

        permit_dnswl_client list.dnswl.org=127.0.[2..14].[2..3]

        which does not explicitly permit email marketing providers nor any IP
        with trustworthiness score of 1. A score of 1 is equivalent to a
        SpamAssassin score of -1, which does not merit a direct shot to the
        queue. That would typically require an SA score of -5. I want these
        clients to go through all of my other restrictions before allowing their
        payload into my queue.

        Also worth noting, there are currently only 14 categories (3rd octet of
        a reply), so specifying 255 is not necessary, and possibly problematic.
        Hypothetically, if dnswl decided one day to create categories 16,
        political campaigns, and 17, religious newsletters, you are currently
        setup to automatically permit such clients.

        Remember, the sole purpose of whitelisting is to bypass all of your
        other spam checks and get the mail into your queue unmolested. IMO, not
        every IP listed by dnswl is deserving of this honor, not even close to
        all of them.

        See section "Return codes" at: http://www.dnswl.org/tech

        --
        Stan
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