I've just found a new and interesting spam source - legitimate bounce messages

[RW]

On Thu, 16 Oct 2008 08:54:55 -0700 (PDT)
Luke Dean <LukeD at pobox.com> wrote:

> 
> 
> On Thu, 16 Oct 2008, Matthew Seaman wrote:
> 
> > Until the wonderful day that the entire internet abides by these
> > rules[*], use
> > of technologies like SPF and DKIM can discourage but not entirely
> > prevent the spammers from joe-jobbing you.
> 
> I just started getting these bouncebacks en masse this week.
> My mail provider publishes SPF records.

SPF increases the probability of spam being rejected at the smtp
level at MX servers, so my expectation would be that it would exacerbate
backscatter not improve it. 

Many people recommend SPF for backscatter, but I've yet to hear a cogent
argument for why it helps beyond the very optimistic hope that spammers
will check that their spam is spf compliant.