On 09/08/2011 19:18, Gary Chambers wrote:
All,
I apologize in advance for this Postmaster 101 question.
Am I correct in understanding that every mail server that is 1) attempting
to deliver e-mail to an invalid address on my server and 2) is from=<>, and
3) the message did not originate on my server is improperly configured?
IOW, if every postmaster configured their mail server to reject mail to an
invalid recipient, would backscatter no longer exist?
Not quite. The bounce mechanism is a key part of how SMTP works, and
there will always be occasions where it is used legitimately. You are
perfectly correct to say that a correctly configured server should never
accept mail for an invalid recipient, and that the majority of
backscatter is caused by servers which fail to follow this principle.
However, there are plenty of reasons why a server might accept mail for
a valid recipient but then be unable to complete the final delivery due
to circumstances which it is unable to test prior to accepting the mail.
Common examples include a mailbox which is over-quota and anti-spam
systems which use content-inspection, while less common examples include
hardware failure and stale Recipient Address Verification (RAV) caches
which happen to coincide with a validity change at the destination.
Carefully managed, it's possible (and desirable) to minimise bounces
caused by all of these, but you can never guarantee that they will not
occur. And, since in all these cases it's important for any legitimate
sender to know that delivery has not been completed, sending a bounce is
equally unavoidable in a properly-configured system.
In any case, backscatter is only a problem because, historically, it has
been indiscriminate and uncontrolled. The occasional misdirected bounce
isn't an issue; it only becomes a problem when it's a large volume.
Trying to eliminate backscatter entirely, therefore, is neither
necessary nor desirable. Provided you eliminate all the avoidable causes
of misdirected bounces and minimise the number of unavoidable ones then
you've got a system which is properly configured.
Mark
