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.


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