AT&T's business customers' were unengaged through email, since their old and out-of-date user preferences were used to send them highly irrelevant email. Previous re-engagement emails were summarily ignored by their customers, as they were a hair uninspiring.
A single email re-engagement campaign that displayed the benefits of updated preferences, in a humorous and relevant manner. This email had 11 points of personalization, so if your name was, say, Agnes, the email would read "Agnes-like: (adj.) Having qualities that Agnes likes." Or Rufus-like, or Jenny-like, or Cody-like, etc.
The clickthrough rate was an astonishing 140% higher than the control version, with a 32% lift in open rates vs. the control.