• by George Bilbrey , Op-Ed Contributor, July 14, 2015

While conducting a recent study of frequency’s impact on email marketing performance, we found again and again that one key factor played a critical role in how volume affected response: mailbox type. When it comes to finding the right sending frequency to maximize subscriber engagement without generating excessive complaints, marketers can gain a real advantage by knowing whether subscribers are reading commercial mail in their primary accounts.

Getting frequency right is important. Undermailing leaves money on the table -- potentially, a lot of money when you calculate the impact on customers’ lifetime value of failing to generate as many orders as possible. Overmailing destroys the lifetime value of your subscriber file, potentially generating a short-term performance lift at the expense of ending relationships with customers who complain or disengage. In fact, severely overmailing to the point where complaints jeopardize deliverability can sacrifice your future without generating any near-term gain.

Your subscribers are the sole arbiters of whether they feel over- or under-mailed, and the account where you reach them turns out to have a powerful influence on how they feel. In our sample, commercial email sent to primary accounts -- the ones people checked at least daily -- was the most sensitive to frequency adjustments. They represented the biggest opportunity for marketers, accounting for 83% of all messages read, but they also represented a disproportionate number of complaints when frequency changed.

Despite the fact that only 24% of subscribers in the sample appeared to get marketing email in their primary accounts, they lodged roughly half of all spam complaints. That means the most engaged audience — people who clearly want and respond to marketing messages, with the biggest upside for senders that get frequency right — is also the audience most likely to cut off all future contact from senders that get it wrong.

Because primary accounts make up the bulk of campaigns’ readers, it may be tempting to discount the value of secondary accounts that are checked only occasionally. (These accounts may be used mostly to get marketing messages rather than personal or even transactional email.) Our study suggests that secondary accounts can represent valuable, enduring customer relationships.

For one thing, these subscribers are far less apt to complain. They showed a far higher tolerance for frequency testing and generally allowed marketers to send them more mail. It’s possible that they buy at different rates than primary subscribers, potentially ordering less often — which would make it critical to send often enough to be visible in the inbox when these people are finally ready to buy.

For marketers that understand which type of account they’re sending to and what the ideal frequency is for each, the rewards are significant: getting it right represented a 40% incremental revenue lift for brands. Here’s how to work toward frequency optimization and start realizing these gains for your program:

Begin analyzing engagement patterns to understand the composition of your file by primary vs. secondary accounts.

Develop frequency testing protocols for each account type. Pay close attention to negative signals as well as response, and look beyond complaints. Decreasing read rates are early indicators of overmailing.

Take long-time value into account when you evaluate frequency tests. Your subscriber file is a long-term asset, and acquiring names is expensive. The cost of replacing burned-out customers can easily outweigh a quick revenue boost from cranking up frequency.