What are the signals of subscriber fatigue, and how do you address them?

Signals of subscriber fatigue:
— Steadily decreasing open rates over time for a segment
— Increasing unsubscribe and complaint rates
— Declining CTOR despite stable open rates
— Engagement Recency data showing subscribers who haven't opened in 60+ days
— Email client caching: Apple MPP pre-loads pixels, inflating open rates and masking true engagement decline
Mitigation strategies:
— Implement Einstein Engagement Frequency to auto-suppress over-messaged contacts
— Build a re-engagement journey for subscribers inactive for 60–90 days (win-back campaign)
— Offer a preference centre allowing subscribers to choose frequency/topics
— Sunset non-engagers: suppressed contacts inactive after 6–12 months improve deliverability for the active list
— Reduce send frequency for low-engagement segments while maintaining high-value content quality