Identifying spammers in your shared web service (featuring Postfix, auditd, and iptables)

Over the last week, we’ve been having a problem with spam in our shared web service: Something was sending out lots of low-quality, easily-blockable spam, and the bouncebacks were filling up the Postfix queues in our outgoing email cluster.  The way we tracked down the spammer was interesting, so I’m writing it up here in case it’s of interest to anyone else!

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