This report provides interactive marketers with advice on email marketing performance management, with a focus specifically on list maintenance. We've outlined a basic formula for calculating email subscriber value (ESV) to help justify budgets and plan messaging strategies. But we also recommend pursuing advanced ESV models that pull in factors beyond tangible sales — such as brand lift, cross-channel acquisition and engagement, and cost avoidance. This report is an update to "What's An Email Subscriber Worth?" originally published on February 1, 2012.