To be alive during the late 19th century would have been positively electric. Maxwell was codifying theories, Edison and Tesla were duking it out over currents, and Faraday had a shocking obsession with cages. All the while, a German man by the name Heinrich Rudolf Hertz was laying the groundwork for what would become wireless transmission by radio. That name should ring a bell. The term “hertz” is used today when discussing cycles per second, or frequency, as a scientific unit.

Hertz’s eponymous standard notwithstanding, early radio transmissions were broadcast using amplitude modulation (the “AM” in AM radio). From Herbert Morrison’s, “Oh, the humanity!” to Orson Welles’ infamous “War of the Worlds,” these are the nostalgia-inducing broadcasts we still hear from time to time. As radio technology continued to develop, frequency modulation (the “FM” in FM radio) overtook amplitude modulation as the modus operandi for commercial broadcasts and remains one of the most prevalent means of delivering top 40 hits to people all over the world.

So, what can email marketers learn from the evolution of radio? For one, amplitude modulation can be thought of as the volume of email sent at any one time. Conventional wisdom says the more email you send, the more chance you have of converting customers. That means the companies with the biggest lists should win hands down. But they don’t, because there are other potential pitfalls marketers must take into consideration.

A larger list compiled solely to include the most possible email addresses could mean a higher number of spam traps. That could hurt deliverability. Even without spam traps, untargeted mass mailings can cause more customers to hit the ‘This Is Spam’ button, or simply unsubscribe. That’s no good either. So, it’s clear that sending the right amount of email is key to engaging an audience, but what else can be done?

Enter our old radio friend frequency modulation. In modern parlance, you might call it frequency optimization. You know intuitively some of your customers love daily deals. Some are more interested in a weekly update. And still others only want to know when a big event is coming up. Savvy email marketers are segmenting and targeting customers not only by traditional demographic and purchase history data, but by more general behavioral patterns like how often subscribers wish to be contacted.

As discussed, over-sending to your lists can have negative consequences. But you might be interested to know your most actively engaged customers tend also to be the most sensitive to change. Research shows that while actively engaged users might make up a small portion of your total list, they tend to generate the vast majority of all reads. Beware, the same audience will not hesitate to complain if a message doesn’t appeal to them. The lesson? If someone trusts your brand enough to sign up for mailings using their primary email account, they are expecting you to treat them with care. That means email should be tempered in volume, tailored with content, and it should arrive on time, every time.