Marketers have been using email as a way to communicate with customers and prospective customers for many years now. As a marketing channel, email has consistently had the highest return on investment. That’s partly because email is so cheap that it’s practically free.

And because email works so well, it has often been the case that we, as marketers, come back to it again and again. Adding a new email to our existing campaigns is cheap and easy. And so we do, often without asking ourselves if it’s too much.

But at a certain point, logic would suggest, it is too much. We are emailing people too often, and driving them crazy in the process. When a company emails you too often as a consumer, you are turned off. When that happens, marketers risk sowing ill-will among their subscriber base and potentially losing customers in the process.

It should be obvious, but we want to avoid that. But how? How do we know when we are emailing too often? Where is the line between not emailing enough, and emailing too much?

The answer is simple: we test.

We already test everything else about our emails…

  • Subject lines
  • Content
  • Links
  • Offers

Why wouldn’t we test frequency?

When we test our emails, we are measuring which versions deliver better results. In a subject line test, we are measuring open rates. The subject line with the highest open rate wins.

In a content test, we are measuring click-through rates. Whichever design gets more people to click through to the website wins.

In a frequency test, we have to measure several metrics at once. First, we have to measure opt-outs and complaints. These are the best metrics email marketers have to measure how many people are turned off by emails. When someone takes action to unsubscribe or mark an email as spam, they are signaling to the company that this email crossed the line in some way.

But that’s not all we have to measure, because opt-outs and complaints rising do not, be themselves, tell us if our strategy is working. For that, we also have to measure conversions. A conversion might be a sale, or a donation, or a click through to an article – whatever you want your recipient to do. This is the ultimate success metric.

If opt-outs and complaints go up, but conversions also go up, your frequency test is still a winner. Because the new frequency is leading to a higher ROI, even if it’s turning some people off.

If opt-outs and complaints go up, and conversions stay flat or drop, your frequency test is a loser. Adding more emails did not lead to any measurable improvement in business outcomes. And you should go back to the old email strategy.

It’s that simple. Now that you know how to test whether you are emailing enough, start emailing more.