Definition
Reach measures the number of unique subscribers who received at least one email campaign during a given period. Frequency measures the average number of campaigns each reached subscriber received in that same period. Together, these two metrics describe the breadth and intensity of a brand's email presence in subscribers' inboxes — comparable to reach and frequency metrics in advertising.
High reach with low frequency suggests a growing list that is being contacted conservatively. High frequency with declining reach suggests list contraction, possibly driven by unsubscribes from over-sending.
How to Calculate
- Reach: Count unique email addresses that received at least one campaign in the period
- Average frequency: Divide total campaign sends across all subscribers by the reach count
- Frequency distribution: Analyse how many subscribers received one campaign, two campaigns, three campaigns and so on — averages can hide important patterns
Why It Matters
This matters because the choices you make here show up directly in your results. High frequency with declining reach suggests list contraction, possibly driven by unsubscribes from over-sending. When this is handled well it supports engagement, delivery, and the trust subscribers place in your brand; when it is neglected, the effects tend to show up in declining performance and harder-to-fix problems further down the line.
Best Practices
- Track reach and frequency by subscriber segment, not just in aggregate — different audiences have different tolerance levels
- Watch for frequency spikes that correspond with engagement declines
- Use frequency distribution data to identify audiences receiving too few or too many campaigns
- Balance reach and frequency against engagement metrics; more sends only help if the additional exposure drives incremental value
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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.
Abuse Complaint
An abuse complaint is a report from a recipient who marks an email as spam, which negatively affects sender reputation and deliverability.
AI Email Summary
An AI email summary is a short, machine-generated overview of an email's key points, shown by Gmail, Outlook and Apple Mail before a recipient opens the message. It is reshaping how email marketers think about subject lines, preview text and open rates.
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.
Frequently Asked Questions
Good practice here means handling Email Reach and Frequency in a way that is relevant, timely, and honest for your audience. Reach and frequency measure how many unique subscribers are exposed to campaigns and how often — two levers that directly affect engagement, fatigue and list health. Done well, it improves engagement and builds trust; done poorly, it creates friction that costs you results.
Because it touches the parts of email that drive outcomes: relevance, trust, and delivery. Small improvements compound, while repeated mistakes quietly erode the health of your programme.
The most common problems are treating Email Reach and Frequency as a one-off task, ignoring what the data says, and copying competitors without testing. All three lead to effort that does not translate into better results.
Compare the metrics it should influence — engagement, conversions, and deliverability — before and after you make changes. Trends over time matter far more than any single send.
It supports the same goal as the rest of your email programme: the right message to the right person at the right time. Aligned with segmentation and automation, it reinforces everything else rather than competing with it.