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
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
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.