Re: MTS transparency and anonymity

> On Mon, 28 Feb 2005, Keith Moore wrote:
> >
> > could you explain the backscatter problem?  I'm not sure what you're referring
> > to.
> 
> If a spammer or a virus sends out forged email (a "joe job") a certain
> proportion of it is likely to be rejected, e.g. because of incorrect
> recipient addresses or anti-virus or anti-spam or anti-forgery checks. If
> the rejection results in a bounce message the bounce will be sent to the
> apparent sender of the message, who is an innocent third party and the
> victim of the joe job. These bounces are backscatter from forged spam, aka
> collateral spam.

the best way I know to deal with that problem is to recognize bounces
(not just by return-path but by message format) and to correlate them with
a Sent IMAP mailbox.  bounces that don't match outgoing mail are silently
discarded.  of course, not everybody use IMAP, and not all IMAP clients 
support storing sent mail in a Sent mailbox.

more ideally, return-paths would be authenticated (in the sense that the 
sender needs to be able to demonstrate he has the right to use that 
return-path), and MTAs wouldn't bounce messages that failed authentication.

Keith