This MediaPost article, True Cost Of An Email Campaign by the CTO of Eloqua, contains some interesting ideas and is a worthwhile read.  But the author’s “Disengagement Path” concept is bogus — disengagement, like engagement, doesn’t happen gradually and linearly.  We know this because Recency (from RFM) response curves aren’t straight lines, they’re usually more like cliffs.

This tells us customers become disengaged much more suddenly, and for reasons that sometimes have nothing to the do with the email they’ve been sent.  Reengagement takes more than just not sending them email for a while (as the article implies), instead we craft targeted campaigns specifically designed to restore lapsed interest.