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.
Best Practices
- Start with the fundamentals of Subscription Fatigue Index and build from a clear baseline, so later improvements are measurable rather than assumed.
- Keep Subscription Fatigue Index consistent with how the rest of your email programme works, so no single initiative works against another.
- Review how Subscription Fatigue Index is handled in your own data and adjust from what you see, rather than copying what another brand does.
- Test one change at a time and measure the effect before rolling it out more widely.
- Revisit your approach to Subscription Fatigue Index regularly, because audience behaviour and inbox technology keep moving.
- Make sure the basics — relevance, timing, and honesty — are solid before chasing more advanced tactics.
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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.
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.
AI Inbox Summary
An AI inbox summary is an AI-generated digest that condenses unread email — often highlighting news, actions and senders — changing how clearly your marketing email reaches and engages subscribers.
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 Subscription Fatigue Index in a way that is relevant, timely, and honest for your audience. Subscription fatigue index measures the risk of over-sending to your list by combining send frequency, engagement decline, unsubscribe rate, and spam complaint trends into a single score. 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 Subscription Fatigue Index 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.