--On 18 October 2006 13:34:50 +0100 Andrew - Supernews
<andrew@???> 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
