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From Matt <lm7...@gmail.com>
Subject Re: thanks to thinking people.
Date Mon, 19 Jul 2010 21:09:57 GMT
> Blocking outbound 25 from the rest of your network, and disallowing submission to your
MX on 25 from your network
>, does very little for keeping your own MX from sending spam which is what SA on outgoing
SMTP would be for.
> It's great from a policy standpoint and contains the "simple" bots, but for keeping your
outbound from MX clean,
> not so much.


In Exim you can ratelimit SMTP connections like so:

http://www.exim.org/exim-html-current/doc/html/spec_html/ch40.html#SECTratelimiting

# Slow down fast senders; note the need to truncate $sender_rate
# at the decimal point.
warn ratelimit = 100 / 1h / per_rcpt / strict
    delay     = ${eval: ${sg{$sender_rate}{[.].*}{}} - \
                  $sender_rate_limit }s

Sure there are ways of doing this with other MTA's as well.

Since spam depends on many thousands of messages this effectively
limits the usefulness of your MTA for sending spam.  Must also limit
the number of connections per IP.  I also think this examples 100
recipients per hour is to low.

Matt

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