Definition
An email list decay model projects how subscriber engagement, deliverability, and revenue contribution will decline over time if no intervention occurs. Decay models account for natural churn, subscriber aging, email address abandonment, and accumulating disengagement. They help quantify the value of list hygiene activities, justify investment in re-engagement programmes, and set realistic expectations for organic list performance. A typical model might show a list losing 20-30% of its engagement value per year without active maintenance.
Model Inputs
- Monthly organic churn rate (unsubscribes, bounces, disengagement)
- Engagement decay curve per subscriber cohort
- Hard bounce accumulation rate from address aging
- Spam complaint escalation from disengaged subscribers
- Deliverability degradation from declining list-wide engagement signals
Best Practices
- Build the decay model from at least 12 months of historical list data
- Validate model predictions against actual outcomes quarterly
- Use the model to calculate the value of hygiene activities by comparing projected decay paths with and without intervention
- Segment decay rates by acquisition channel to identify which sources produce the most durable subscribers
- Include decay projections in quarterly list health reviews and growth planning
Related Glossary Terms
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.
Dynamic Content
Dynamic content in email refers to content blocks that change based on subscriber data, behavior, or preferences within a single email send.
Email Account Health Score
A composite metric that evaluates the overall health of an email sending programme based on deliverability, engagement, list quality, and compliance factors.
Email Active Subscriber
An active email subscriber has opened or clicked an email within a defined recency period, typically 30-90 days by industry. Active subscriber rate of 40-60% is typical for healthy email lists.
Email Browser Push
Comparing email marketing with browser push notifications as complementary channels for subscriber engagement and re-engagement.
Email Campaign Breakeven Analysis
Calculating the minimum conversions or revenue a campaign must generate to cover all costs including creative production, ESP fees, and team time.