On Fri, 6 Dec 2002, Philip Hazel wrote:
> In Exim 4.11 (out soon) you will be able to specify a delay in the ACL.
This is already possible by writing something like
condition = ${run{/bin/sleep 59}{1}{0}}
in an ACL. (I found that you time-out the command after 60 secs,
hence the limit). Add more lines like that to the ACL to delay
longer.
> This, I guess, will provide a form of teergrubing.
If you just keep repeating 59sec delays, without sending any kind of
response, the other host will typically give up after ~ 5 mins. (I'm
actually using this to drop those annoying dictionary-scan attacks,
which steadily plough their way through a couple of dozen random
addresses - ignoring the 5xx responses telling them they're
blacklisted as an open proxy - and filling-up our rejectlog with
junk.).
> Is there anything more to it than "delay before responding"? Hmm. I
> suppose you could send a multi-line response, delaying before each
> line...
Bingo.
