public blacklists

[Ed Wilts]

On Thu, Dec 09, 2004 at 10:06:32PM +0800, Ow Mun Heng wrote:
> In that case, in some cases, eg: if one runs their own mail-server,
> grey-listing seems to be a better option compared to spamassassin, even
> when using SURBL.
> 
> Reason being, greylisting stops it at the MTA level, spamassassin only
> tracks it once it's already in the system.

greylisting doesn't stop it all.  There are a bunch of well-behaved mail
servers out there sending spam and if you don't have spamassassin or
some such tool installed, you will get spam.  I turned on greylisting
last night on my home server and still had 10 spam messages by morning
that spamassassin/procmail had delivered to by spam folder.

A coworker turned on greylisting on his home system last night and
discovered that a message from the mrtg mailing list was initially
blocked but not retried.  In other words, a legitimate message that
should have been delivered went to the bit bucket.  You can make a
perfectly valid case that the server that tried to deliver it is broken,
but you can also make a perfectly valid case that you're now preventing
legitimate e-mail from being delivered.  Yes, you can add specific hosts
to a whitelist but that requires manual maintenance and sometimes can't
be detected until *after* you've prevented delivery.  In a large
corporate environment, it's too late to add a server to a whitelist -
you may have already lost an order, frustrated a customer, or at least
added maintenance work for your e-mail admins.

There is no single free one-step method for stopping all spam and
nothing but the spam.

-- 
Ed Wilts, RHCE
Mounds View, MN, USA
mailto:ewilts at ewilts.org
Member #1, Red Hat Community Ambassador Program