On Thu, Aug 27, 2009 at 10:06:03AM -0500, Shawn McKenzie wrote:

> Paul M Foster wrote:
> > On Thu, Aug 27, 2009 at 09:00:24AM -0400, Bob McConnell wrote:
> >
> >> The return code only tells you the local server accepted the mail. It is
> >> unlikely that server knows the address is invalid since it can only
> >> validate the domain portion of the address. Only the destination server
> >> can validate the user name, and most are now configured not to report
> >> mail sent to invalid addresses due to spam. They will silently discard
> >> the message.
> >>
> >
> > It used to be that internet mail servers would deny an email address as
> > invalid while the SMTP conversation was going on. Then, because of
> > services with millions of addresses, like Yahoo, they stopped doing
> > this, and instead would bounce the messages back some time later.
> >
> > I recently had a conversation with a guy who's heavily involved in
> > internet email. His view echoed what you're saying-- it does spammers a
> > favor to bounce messages to bad addresses. But I got the impression that
> > his view was a minority one.
> >
> > It sounds like you're saying his view has become the majority view. Does
> > your job put you in a position to confirm this with authority?
> >
> > Paul
> >
> It's called backscatter spam and the problem is this:  if a spammer uses
>   someones legitimate address, let's say yours as the from address, and
> sends to thousands of recipients, then you get all of the failure
> messages.  If that's not bad enough, consider if the from address is a
> legitimate domain but nonexistent user, then the server that receives
> the failure messages sent to the nonexistent user may issue its own
> failure messages back to the other nonexistent users, and maybe back and
> forth either infinitely or until some server reaches a configured
> threshold of some sort.

Believe me, I know about backscatter. I'm admin on about six lists, and
my email address is on at least five public websites. You want
backscatter? I got backscatter.

The worst case (not necessarily backscatter) was when I had a backup
admin on one of those lists, and majordomo was issuing bounces to both
the backup and me. Unfortunately, at the same time, his email address
went down. Now I was getting bounces of the bounces from his email
address too. And each email contained the text of the previous bounce.
So I was getting 250k (size) emails (and growing) as fast as majordomo
could generate them. I had to call the host company for the lists to get
them to take him off as an admin.

I just love computers. ;-}


Paul M. Foster

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