For years, email performance has been measured with a familiar set of metrics: opens, clicks and conversions. But those numbers are becoming less useful — not just because of privacy changes, but because mailbox providers (MBPs) are now judging emails the way users do: based on engagement, trust and intent. That shift is forcing marketers to rethink how they measure success. A new report from Validity points to three emerging metrics that are likely to go mainstream in 2026 — and they say more about subscriber relationships than traditional KPIs ever could. ## 1. Disaffection index signals when audiences are tuning out The first metric flips the usual performance mindset on its head. Instead of focusing on positive engagement, the disaffection index measures the signals that indicate an audience is losing interest — combining unsubscribes, complaints and bounces into a single metric.…