Definition
Open reach counts how many distinct subscribers opened any campaign over a defined timeframe, typically a week or month. Unlike campaign-level open rate, which tells you how a single email performed, open reach tells you how many of your subscribers are actively engaging with your email programme at all.
This metric is particularly valuable for assessing overall list health. If open reach is declining while per-campaign open rates remain stable, it means the same engaged subscribers are opening but the broader list's engagement is narrowing — a warning signal that churn may follow.
How Open Reach Complements Per-Campaign Metrics
A campaign may show a consistent 25 percent open rate month over month. But if open reach declines from 10,000 unique openers to 6,000, the same rate is being sustained by a shrinking audience. Open reach catches this pattern before it manifests in revenue decline.
Best Practices
- Track open reach monthly alongside total list size to monitor the engagement ratio
- Segment open reach by acquisition source to identify which channels produce the most consistently engaged subscribers
- If open reach declines while list size grows, review onboarding and welcome sequences — new subscribers may not be activating
- Set open reach targets as part of list health KPIs rather than focusing exclusively on campaign-level metrics
Related Glossary Terms
A/B Testing
A/B testing in email marketing is the practice of sending two variations of an email to a small sample of your list to determine which version performs better before sending the winner to the remaining subscribers.
Abandoned Cart Email
An abandoned cart email is an automated message sent to customers who added items to their online shopping cart but left without completing the purchase. It is one of the highest-converting email types in ecommerce.
ARPU (Average Revenue Per User)
ARPU (Average Revenue Per User) is a metric that measures the average revenue generated per email subscriber over a specific period, used to evaluate list value and campaign effectiveness.
Attention Rate
Attention rate is the percentage of email opens that last longer than 5 seconds, distinguishing genuine reads from passive opens, preview-pane views, or Apple MPP auto-loads.
Bounce Rate Threshold
A bounce rate threshold is the percentage of hard or soft bounces at which email platforms and ISPs begin to penalise sender reputation, typically around 2-5%.
Bounce Rate
Email bounce rate is the percentage of emails that were rejected by the receiving server before reaching the recipient. It is a key indicator of list health and data quality.