On Fri, 26 Feb 2010, Andrew Hearn wrote:

| However, is there a way to ratelimit or deny hosts based on how many
| messages they've sent that have been rejected/deferred by the recipients MX?

We do this.  Local senders who trip a limit are added to a list such that 
everything they send is frozen, until a human can investigate.

I'm not aware this can be achieved purely inside Exim.  Our setup is based 
on a custom-written log watching script.

The idea came from Richard Clayton's "Stopping Spam by Extrusion 
Detection" paper:

 http://www.cl.cam.ac.uk/~rnc1/extrusion.pdf

and I'm happy to report it's been very effective at cutting off spam runs 
long before any significant damage to repuation occurs.

-- 
Chris Edwards
IT Security, Computing Service
University of Glasgow, charity number SC004401

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