--On 18 October 2006 13:34:50 +0100 Andrew - Supernews 
<[EMAIL PROTECTED]> wrote:

>
> (I say "perceived" because I am skeptical about the proportion of spam
> that actually fails callout verification.)
>

As a quick snapshot, one of my four MX hosts has rejected 41,000 messages 
today, of which 15,000 were sender verification failures. In the same time, 
it accepted 4,600 inbound messages. These are messages that have passed RBL 
tests and HELO string checks.

So, even if we assume that all the inbound messages were spam, sender 
verification is blocking about 75% of spam that pass our IP and HELO tests. 
If we assume that some of the inbound messages are ham, then sender 
verification is better than 75% effective for us. So, don't let anyone tell 
you that spammers tend to use valid sender addresses. Presumably the more 
efficient ones might, but they're not usually using their own resources 
anyway.

-- 
Ian Eiloart
IT Services, University of Sussex

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