Definition
The subscription fatigue index tracks whether your sending frequency is approaching the point where subscribers start disengaging. It rises when send frequency increases without a corresponding increase in engagement, signalling that recipients are becoming overwhelmed.
Components
- Send frequency: Emails per week per subscriber
- Engagement trend: Are open and click rates declining relative to send count?
- Unsubscribe rate: Are more people leaving after each send?
- Spam complaint rate: Are more recipients marking mail as spam?
- Quiet period: How long before a subscriber who used to engage becomes inactive
Why It Matters
Pushing past the fatigue threshold damages long-term deliverability and list health. Monitoring the fatigue index helps you find the optimal frequency before subscribers start tuning out or reporting spam.
Related Glossary Terms
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.
Campaign Lifted Revenue
Campaign lifted revenue is the additional revenue generated by an email campaign beyond what would have occurred without it, measured via a holdout group or statistical lift analysis.