Author: Thomas Fini Hansen Date: To: exim-users Subject: Re: [beast@system-tnt.dk: Re: [Exim] Exim 4.32 Released]
On Fri, Apr 16, 2004 at 09:47:09AM +0100, Philip Hazel wrote: > On Thu, 15 Apr 2004, Thomas Fini Hansen wrote:
> > What kind of problems showed up?
>
> The problem was a huge increase in the number of callouts, particularly
> for incoming spam, where the sender address tends to be different every
> time. If you know that the receiving host does not make any use of the
> sender while verifying, then it makes sense to use <> as the sender, so
> that the cache reduces the number of callouts when you get lots of
> messages for the same recipient.
Aaah, of course. So in theory, one could have a spam dictionary attack
echo through a powerful frontend server and bog down a server
behind. Out of curiosity, anyone tried that? Some form of throttling
of callouts might help in those situations. I guess one could
experiment with that using readsocket and a little daemon.
