Date: Mon, 2 Apr 2007 17:36:25 -0600 (MDT) From: Warren Block <wblock@wonkity.com> To: Angelin Lalev <lalev@uni-svishtov.bg> Cc: freebsd-questions@freebsd.org Subject: Re: advice on anti-spam tools Message-ID: <20070402172704.K35632@wonkity.com> In-Reply-To: <0875b56eeca4d320fd9fa7b0d940fce2@uni-svishtov.bg> References: <0875b56eeca4d320fd9fa7b0d940fce2@uni-svishtov.bg>
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On Tue, 3 Apr 2007, Angelin Lalev wrote:
> My e-mail server is running the latest spamassassin with all of the blacklist enabled and etc.
> but I still receive over 20 spam messages a day ("image" spam mostly).
> The situation with other users may be worse. That's why I was thinking about some tool that
> 1. store incoming email
> 2. send request to the sender of the message, requiring to go to some address and enter the numbers (letters)
> from image
> 3. if the puzzle is solved in time (week or so) deliver the message, otherwise delete it.
This is called "challenge-response". The headers of the spam
are almost certainly forged and can't be trusted.
So it's impossible to really tell the sender of the message. Your
"challenge" will be spam sent to an innocent person whose From: address
was forged in the original.
A quick search of ports doesn't show any obvious challenge-response
software.
If you're not already using greylisting, consider that.
-Warren Block * Rapid City, South Dakota USA
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