Email Metrics Marketers Often Misinterpret

When marketing teams evaluate their email campaigns, they instinctively turn to two familiar figures: open rate and click-through rate (CTR). While these metrics offer a surface-level view of engagement, they frequently fail to reveal whether an email program is delivering meaningful business results. Relying on them as primary key performance indicators (KPIs) can steer optimization efforts toward the wrong goals entirely, misleading teams about what truly drives success.

The evidence against using these engagement metrics as reliable success signals is compelling. In numerous subject line A/B tests conducted across diverse clients and audiences, the version achieving the highest open rate often generated fewer conversions or a lower revenue per email (RPE). Similarly, campaigns with the highest CTR frequently underperformed in driving actual business outcomes. This pattern isn’t incidental, it’s a consistent finding from years of methodical testing.

Consider open rate as a KPI. Many teams use it to judge subject line effectiveness, but it’s a poor proxy for conversions or revenue. Analysis of scientific A/B tests reveals a troubling pattern. When marketing departments depend on open rate to guide their testing, it correctly identifies the highest-converting version only 20% of the time. It points to the wrong winner 10% of the time. Most critically, in 70% of tests, open rate variance falls within the margin of error, rendering it inconclusive even when a clear performance winner exists. In total, open rate either misled the analysis or provided no useful insight in 80% of evaluated cases.

The situation with click-through rate is even more problematic. One might assume clicks, occurring later in the customer journey, would correlate more strongly with final outcomes. The data contradicts this assumption. In campaign tests comparing CTR to conversion rate or RPE, the highest-clicking version also produced the best business result a mere 7% of the time. It identified the incorrect winner 36% of the time. In 57% of tests, CTR differences were statistically insignificant despite clear variances in business metrics. This means CTR reliably indicated the true campaign winner only 7% of the time.

If these common engagement metrics are so unreliable, what should marketers measure? True email performance is best evaluated by metrics that track concrete results. The two most critical are conversion rate and revenue per email.

Conversion rate measures the percentage of recipients who complete the intended action, answering the fundamental question of whether an email caused the desired behavior. A conversion can be any valuable action, from a purchase or demo request to a webinar registration or app download. The formula is straightforward: Conversions divided by the number of delivered emails, expressed as a percentage. This metric directly ties campaign effort to goal achievement, making it the superior KPI for initiatives designed to drive specific actions.

For ecommerce and sales-driven programs, revenue per email (RPE) is the ultimate metric. Calculated as total attributable revenue divided by delivered emails, RPE provides a direct dollar figure linking email activity to financial impact. This focus often uncovers insights hidden by engagement data. A telling example involves a company selling premium audio equipment. They tested whether to include product prices in their emails, using CTR as their KPI. The version without prices generated significantly more clicks and was declared the winner. However, this likely spurred “curiosity clicks” from recipients seeking price information, not necessarily clicks from serious buyers. Without tracking conversions or RPE, the team had no way to know which version actually drove more sales, making their test conclusion fundamentally questionable.

The essential takeaway for modern email marketers is clear. Open and click-through rates retain value as diagnostic metrics for understanding user interaction with content. They should not, however, serve as the primary KPIs for most programs. When business goals center on conversions and revenue, performance must be measured against those outcomes directly. This requires a disciplined focus on conversion rate to gauge campaign effectiveness and revenue per email to quantify financial return. Ultimately, opens and clicks do not define a campaign’s success, tangible outcomes do.