You know what I would like to see is a means of sending back a message on confirmed Spam that carries the "550 User Unknown" designation and a "from" address appearing to be [EMAIL PROTECTED] (whatever it was) to make it appear believable.
I realize that a goodly number of these would bounce because the sender had a bogus address and/or domain and possibly you could only do this when the Reverse DNS lookup actually worked, but since the bounce will come back through declude you could plant a header that you could detect and simply cause the message to be discarded when it comes back (the bounce confirming it was spam). This would possibly make some of the spammers remove the apparent "bad addresses" - if any actually do that.
Although this sounds like a good plan (and some people have done it before), it just doesn't work. Spammers don't care about bounce messages, and they don't treat unsubscribe requests as proof that an E-mail address works (we've sent a number of E-mail addresses to spammers' unsubscribe links, and never seen a single spam as a result).
And, about 99% of the time, the spammer will never even get the bounce message. It is very rare for a spammer to use a valid return address.
Another thought. Would it be possible, if not too much overhead, to do an SMTP HELO connect to the alleged sending server and verify the sending email address actually exists in the domain (after confirming the domain exists of course)?
It would be possible, but there are a number of drawbacks (if you check the archives of this list, there was some information posted in the past few days about this).
-Scott
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