From: Paul M Foster

> 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
>> unlikely that server knows the address is invalid since it can only
>> validate the domain portion of the address. Only the destination
>> can validate the user name, and most are now configured not to report
>> mail sent to invalid addresses due to spam. They will silently
>> the message.
> It used to be that internet mail servers would deny an email address
> 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
> favor to bounce messages to bad addresses. But I got the impression
> his view was a minority one.
> It sounds like you're saying his view has become the majority view.
> your job put you in a position to confirm this with authority?

No, it doesn't. However, as part of my job I have monitored several
security lists. When SPAM generators, that had been widely deployed by
virus, started sending mail with random return addresses, they forced
another change in the email admin best practices discussion. For a short
while the network became clogged in bounce messages sent to both valid
and invalid addresses. Some of the invalid addresses even triggered
infinite loops of error messages. None of the servers I am familiar with
send bounce messages reporting invalid addresses any more. Our own
servers won't even tell us internally when they discard incoming
messages. SPAM quarantine is a thing of the past.

Bob McConnell

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