From: /dev/rob0 (rob0gmx.co.uk)
Date: Mon Aug 14 2006 - 12:56:22 CDT

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On Monday 14 August 2006 12:51, Alejandro Kurchis wrote:
> Dear all, I'm using Postfix as my MTA and Spamassassing as my anti
> spam package in my Linux box.
>
> But I've just read that I can set up an open relay filter in the
> main.cf file, as follow (using ordb.org database):
>
> maps_rbl_domains = relays.ordb.org
>
> smtpd_client_restrictions = reject_maps_rbl
>
> My question is:

Before we get to that, it would be a better idea for you to read the
documentation included with YOUR copy of Postfix, rather than finding
random junk on the Web. The syntax you're using is long deprecated.

> Is it a good idea to use an open relay explicit filter in my Postfix
> main.cf file, or does Spamassassin use it by default ???

It's best to reject as much as possible in SMTP before DATA. It's
wasteful (and arguably, spam-friendly) to accept the spam and use
content filtering as you suggest. Furthermore, relays.ordb.org is
insignificant in what it will catch, as spammers are not using open
relays to the extent they once did. See here for more ideas:
    http://jimsun.linxnet.com/misc/postfix-anti-UCE.txt
    http://www.spamhaus.org/effective_filtering.html

In the former, pay close attention to the HELO checks. Those will block
a significant percentage of connections without so much as a single DNS
lookup.
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