[plug] Bounce Spam (Back scatter)

[Adrian Chadd]

A random datapoint about this - UWA suffered from this problem for a few years
as they have a spam/virus scanning mail server sitting in front of the whole
campus. Said mail server didn't know about the users on each of the backend
servers in departments and so would accept the mail and then end up passing on
the generated bounces from invalid email addresses.

And, as you can imagine, the university has a large amount of churning email
addresses and dictionary attempted spam, so a lot of mail was to bad addresses
and bounces from said delivery attempt.

When Grahame turned on the postfix magic to query back-end servers about the
existance of users (and cache the delivery attempt, positive or negative) they
saw an immediate reduction in server load and incoming/outgoing traffic.

So its definitely worth looking into..



Adrian