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The future of e-mail marketing: how to measure true engagement
- Ioana Grigore
- Jan 4
- 4 min read
In 2025, e-mail marketing KPIs are evolving to align with new trends in personalisation, automation, privacy, and AI.
e-Mail marketing continues to evolve as one of the most effective channels for building relationships, driving conversions, and fostering brand loyalty. However, as we step into 2025, the rules of engagement are changing. With shifting consumer behaviours, advancements in AI-driven analytics, and growing concerns about privacy and personalisation, traditional metrics like open rates and click-through rates are no longer enough to gauge success. We need a more sophisticated approach and composite KPIs seem to be the answer.
But before anything, I hope you already know the basic e-mail marketing KPIs you need to keep an eye on:
Open Rate: This measures the percentage of recipients who open your e-mails, indicating the effectiveness of your subject lines and sender reputation.
Click-Through Rate (CTR): The percentage of recipients who click on links within your e-mail, reflecting the relevance and engagement level of your content.
Conversion Rate: The percentage of e-mail recipients who complete a desired action, directly linking your e-mail efforts to business outcomes.
Bounce Rate: The proportion of e-mails that couldn't be delivered to recipients' inboxes. A high bounce rate can harm your sender reputation and indicates issues with your e-mail list quality.
Unsubscribe Rate: The percentage of recipients opting out of your e-mail list after a campaign. Monitoring this helps assess content relevance and e-mail frequency.
Spam Complaint Rate: The percentage of recipients marking your e-mails as spam. Keeping this low is crucial to maintain deliverability and a positive sender reputation.
Click-to-Open Rate (CTOR): The ratio of unique clicks to unique opens, providing insight into how compelling your e-mail content is to those who open it.
List Growth Rate: The rate at which your e-mail list is expanding, indicating the success of your subscriber acquisition strategies.
Revenue Per e-Mail (RPE): The average revenue generated per e-mail sent, helping evaluate the financial effectiveness of your campaigns.
But how does the future look like?
To stay ahead, marketers must adopt a more holistic approach by tracking new, dynamic KPIs that reflect deeper engagement, sentiment, and long-term customer impact. These emerging metrics are designed to provide actionable insights into audience behaviour, uncover hidden patterns, and optimise campaign strategies in real time.
Moving further on, we’ll dive into the innovative KPIs that are redefining e-mail marketing success in 2025—helping you measure not just activity, but genuine resonance and impact. Whether it’s understanding subscriber fatigue, tracking nuanced interactions, or benchmarking against industry trends, these new KPIs are your guide to e-mail marketing excellence in the years ahead.
Engagement Score
This is a composite score that combines open rates, click rates, dwell time, and interactions within the e-mail. It reflects deeper engagement, beyond basic clicks and opens, to measure how well your e-mail resonates with recipients. Since not all metrics have equal importance, the formula contains weights based on your campaign goals.
ES=(OR×w1)+(CTR×w2)+(DT×w3)+(IR×w4)
Open Rate (OR) = e-mails opened/e-mails delivered×100
Click Rate (CTR) =link clicks/e-mails delivered×100
Dwell Time (DT) measures how long recipients spend viewing the e-mail. This can be tracked using e-mail analytics tools and it is expressed as a percentage of average time spent reading e-mails across your campaigns.
Interaction Rate (IR) includes actions like answering polls, filling out forms, interacting with buttons, or engaging with embedded media.
IR=interactive actions/e-mails delivered×100
Example weights:
w1=0.3 (Open Rate)
w2=0.4 (Click Rate)
w3=0.2 (Dwell Time)
w4=0.1 (Interaction Rate)
High engagement score indicates a highly engaging e-mail with content that resonates well while a low engagement score suggests a need to optimise elements such as subject lines, content, visuals, or personalisation. The engagement score can be tailored to include additional metrics like reply rates or social shares, depending on the campaign's objectives. Modern tools often use AI to track these metrics and provide actionable insights.
In order to understand your position against the benchmark break down the engagement score into its components (e.g., open rate, click rate, dwell time) and compare these against industry averages. Then combine the component benchmarks to estimate ranges for your engagement score.
Based on the above weights and component metrics we can estimate:
high engagement around 20–25
average engagement around 10–19
low engagement lower than 10
Tip: Track your Engagement Score over multiple campaigns and monitor trends. Improving upon your own historical averages is often more meaningful than meeting generic benchmarks.
e-Mail Fatigue Index
This is a composite metric designed to measure the signs of fatigue among your e-mail subscribers. It's not a standard KPI, but rather a calculated score derived from a combination of observable behaviours.
EFI=(ORD×w1)+(USR×w2)+(CTRD×w3)+(SCR×w4)+(EOT×w5)
w1,w2,w3,w4,w5 are weights assigned based on the relative importance of each metric to your business goals.
Decline in Open Rate (ORD) indicates whether fewer people are opening your e-mails over time
ORD=(Previous Period Open Rate−Current Period Open Rate)/Previous Period Open Rate×100
Increase in Unsubscribe Rate (USR) highlights if recipients are opting out more frequently.
USR=(Current Period Unsubscribe Rate−Previous Period Unsubscribe Rate)/Previous Period Open Rate×100
Click-Through Rate Decline (CTRD) reflects decreasing interest in your e-mail content.
CTRD=(Previous Period Click-Through Rate−Current Period Click-Through Rate)/Previous Period Click-Through Rate×100
Increase in Spam Complaints (SCR) signals dissatisfaction with your e-mails.
SCR=(Current Period Spam Complaints Rate−Previous Period Spam Complaints Rate)/Previous Period Spam Complaints Rate×100
Drop in Engagement Over Time (EOT) can be defined as the ratio of unique opens and clicks over time.
EOT=Cumulative Decline in Engagement Over Time/Total Engagement Period×100
A high EFI score indicates significant fatigue among your subscribers, prompting a need for changes in your e-mail strategy (e.g., reducing frequency, improving content relevance). A low EFI score means your audience is engaging well with your e-mails.
This metric can be adapted based on your specific e-mail marketing goals and the behaviours of your audience.
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