Sender authentication & zombies (was Re: Time to check the rate limits on your mail servers)

[J.D. Falk]

On 02/04/05, Douglas Otis <dotis@mail-abuse.org> wrote: 

> Attempting to detect spam trickled through thousands of compromised
> systems sent through the ISP's mail servers, SPF does nothing, 

	Nor is it purported to.  Domain-based authentication schemes
	are intended to handle an entirely different problem.

> and could
> actually damage the reputation of those domains that authorize the
> provider for their mailbox domain using SPF.  These records can be read
> by the spammers and then exploited.  Repairing this reputation could be
> next to impossible.

	You touch on some basic realities here:

		1. spam coming out of your network will affect your
		   reputation.

		2. spam coming out of your own mail machines will affect
		   your reputation even more immediately.

	Neither are affected by any of the domain authentication schemes
	currently in play (SPF, SenderID, DomainKeys, etc.)  The spam
	itself may include forgeries, but that's a different issue.

-- 
J.D. Falk                                          uncertainty is only a virtue
<jdfalk@cybernothing.org>                    when you don't know the answer yet