Rule 1: Don't overmail.

Lapsed or disengaged opt-ins represent the majority of most house lists. You can and should develop a program that avoids overmailing people into these two categories, and there are relatively simple ways to do this.

For example, using suppression testing, a retail marketer was able to determine the optimal duration at which to stop sending email to lapsed responders before sending re-engagement messaging. Basically, we simply tested different suppression intervals (one week, two weeks, etc.) until we found the one that drove the highest reactivation. When this optimal timing was put to use, the retailer's re-engagement messaging received double-digit response rates across the board.

In addition, at least quarterly, you need to ensure that your ancillary email streams (opt-in, unsubscribe, ECOA, transactional) meet or exceed the functionality of best-in-class emailers so your list doesn't grow stale.

Rule 2: Don't undermail.

Identify the core customers who respond to your messages almost religiously, but don't let these fanatics dictate your whole program. Design your campaigns around the second-tier of customers who respond frequently -- but not fanatically -- and then add another layer for those core customers. Test your process to learn what will make these users respond more often.

For example, using recency-frequency testing, another retail emailer conducted creative, offer and subject line testing among its most recent responders. As results came in, it became apparent that results were uniformly positive across most tests. The affectionately termed "fanatics" responded and converted almost regardless of the given offer. The team changed course to identify the "frequents," meaning those who reply often instead of always. Extra clicks and conversions from this group accelerated revenue from the entire program, thereby boosting ROI.