> For our userbase with yahoo/hotmail/aol accouts they hit the spam button more often than delete.  Then complain they do not get emails anymore from us, then want discounts on a bill of sale they missed. It is a never ending story.
Ok, that's not an algorithm but I hope you see my point.
one AOL (et al) customer then one could revisit this idea.
to any number of customer-reported problems which ripple outwards.
fire alarm shouting over the house loudspeaker "CALLS COMING IN!"
phone) in the same general location. Then your heartbeat increased.