How to Measure Email Marketing ROI (The Metrics That Matter)

Email measurement has a specific and under-appreciated problem: the metric everyone reports has been broken since September 2021, and the headline ROI figure everyone quotes was never a measurement in the first place. Both are still on the average dashboard and in the average board deck. Fixing your reporting starts with knowing which numbers are evidence and which are decoration.

Apple broke the open rate, deliberately

Mail Privacy Protection shipped with iOS 15 in September 2021. Apple’s own description is blunt: in the Mail app, Mail Privacy Protection stops senders from using invisible pixels to collect information about the user. In practice, Apple Mail fetches remote content, including your tracking pixel, through a proxy whether or not the recipient ever looks at the message, and it masks the IP address so you cannot infer location or device either.

This would be a minor annoyance if Apple Mail were a niche client. It is not. Litmus, which measures client share from over a billion tracked opens, put Apple Mail clients at roughly 46% of opens in its September 2025 data. Roughly half of every open rate you report is therefore a machine fetching an image on a schedule you do not control.

The damage is not just to the number. It is to everything downstream: send-time optimisation trained on open timestamps, engagement segments defined by "opened in the last 90 days," and any A/B test judged on opens. All of them are now partly modelling Apple’s prefetch behaviour rather than human behaviour.

What to report instead

Revenue per recipient deserves the emphasis. It normalises across send sizes, which is the only way to compare a 40,000-person newsletter against a triggered flow that reaches a few hundred people a month. Klaviyo’s benchmark study of more than 143,000 abandoned cart flows sent in 2023 found an average revenue per recipient of $3.65, with the top decile at $28.89. A broadcast campaign does not come close to those numbers on a per-recipient basis, which is the entire argument for investing in automation workflows before investing in more campaigns.

About that $36

The claim that email returns $36 for every $1 spent is repeated so consistently that it reads as measured fact. It is not. The figure originates in marketer self-report surveys. Litmus’s 2025 State of Email survey of nearly 500 marketing professionals found 35% reporting a return between $10 and $36, 30% reporting between $36 and $50, and 5% reporting more than $50. That is a distribution of opinions from people with an interest in the answer, not an audited measurement of incremental revenue.

Email probably does have the best return of any channel a small business can run, for the mundane reason that the marginal cost of a send is nearly zero and the audience opted in. But you should not need a survey to know that, and you should be suspicious of any planning that treats $36 as an input.

The calculation itself

ROI is (revenue attributed to email minus cost) ÷ cost. The part people get wrong is cost. Include the platform subscription, any deliverability or verification tooling, and an honest hourly value for the time spent writing, designing, and QAing. For most small businesses the time cost exceeds the software cost by a wide margin, and leaving it out produces a flattering number that hides the fact that a weekly newsletter is expensive.

Fix your attribution window before you start, not after you see the results. Whether you count conversions within one day or seven days of a click, apply it consistently across every send and every month, otherwise your trend line is measuring your reporting choices.

Valter Brandt

Chief Marketing Officer

Valter Brandt is the Chief Marketing Officer of ThisCom, working with clients across the United States and Europe. He has led marketing strategy through the major shifts in social advertising, mobile, content marketing, programmatic media, and marketing automation.

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