[Exim] Thwarting dictionary attacks

Hi,

A few months back, Ollie Cook posted a patch to implement an
anti-sorted-dictionary-attack ACL:

http://www.exim.org/pipermail/exim-users/Week-of-Mon-20040301/067807.html

Has anyone been using this patch? Does it introduce any stability
problems? Is this the best technique to stop these guys? Our mail
servers are constantly under brutal attacks from these evil bastards.

thx,

Chris Snell