Dictionary Attacks

[Jim Holland]

On Tue, 24 Oct 2006, DAve wrote:

> I am the upstream provider, next stop is MCI. I am seriously thinking
> about using a DUL blocklist. I've tried before but so many shrink wrap
> admins out there running a business on a DSL and using their own
> Exchange, makes it tough. I will surely get complaints when my clients
> can't get an email from someone outside.

If you are being seriously DOS'ed then your clients won't get their e-mail 
anyway.

Other sendmail utilities I forgot to mention that I use are:

	require_rdns

which checks for valid PTR records etc.  I have hacked my version so that
it always gives 451 errors and not fatal errors.  However it does require
lots of manual whitelisting of non-compliant but valid systems, which is a
drag.  I rely on users responding to a daily report on blocked mail that I
send out to contact me for whitelisting.

and
	smf-sav

which does both recipient verification (replacement for milter-ahead) and
sender verification.  A new version (v1.4.0) is coming out tomorrow which
should offer sender verification that is flexible enough to install on a
production system (with the current version I am using recipient
verification only).  It will also have the benefit of slowing down
connections and reducing the CPU load.

Regards

Jim Holland
System Administrator
MANGO - Zimbabwe's non-profit e-mail service