As I mention here: http://news.ycombinator.com/item?id=3476311 http://news.ycombinator.com/item?id=3476311 We use a combination of algorithms and humans to det

As I mention here: http://news.ycombinator.com/item?id=3476311 http://news.ycombinator.com/item?id=3476311 We use a combination of algorithms and humans to determine "unusual" activity (not just spam or forged emails) and act accordingly. We're even proactive about finding customers who break into new send volume thresholds and offer them discounts. We'd much rather have high quality senders in our network for a LONG time than just keep the highest billing rate on autopilot.