Re: Discovering users by RCPT TO
From: Faisal Khan (faisal_at_netxs.com.pk)
Date: Fri, 14 Jan 2005 23:57:58 +0500 To: email@example.com
Turning on Reverse DNS and Tarpitting helps for Dictionary Attacks.
At 09:57 PM 1/14/2005, you wrote:
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>I see spammers hitting my MTA daily with dictionary RCTP TO queries
>and there isn't much you can really do against it; however I have been
>thinking about a solution using real time blockers.
>The idea is to monitor the logfile of the MTA, looking for a host
>getting more than "X" failed destination addresses (I think 2 or 3 is
>a nice entry threshold). Then when they reach the threshold their IP
>gets put into a local DNS server that is used by the MTA to as a real
>This wouldn't' require more than another RBL addition to the MTA and
>then an external script tied to either bind or djbdns.
>Vince Hoang wrote:
>|On Thu, Jan 13, 2005 at 02:20:12PM -0500, Chris Buechler wrote:
>|>I'd recommend disabling it unless you get flooded by such spam
>|>attacks. I would probably consider it unnecessary information
>|>disclosure, depending on the environment and reason (if any)
>|>for doing it that way.
>|Some MTAs allow permit you to drop the session after a certain
>|number of failures, but that only slows down the dictionary
>|You cannot disable RCPT TO because that is how the SMTP protocol
>|designates the recipients.
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