How does engagement decay over time?

Subscriber enthusiasm doesn't evaporate overnight. It fades. Someone signs up, opens a few emails, clicks once or twice, then life moves on. The opens get less frequent. Eventually they stop entirely. That's engagement decay, and it's happening on every list.

The decay curve looks roughly like this: most engagement happens in the first few weeks after signup. After 30 days without an open or click, a subscriber is trending toward inactive. After 60 to 90 days, most programs consider them inactive and either suppress them or trigger a re-engagement campaign. After 180 days, they're often treated as dormant and represent real deliverability risk if you keep sending.

Why the risk? Because mailbox providers watch your engagement signals. A list with a growing inactive segment tells providers that your emails aren't wanted. That gradually pushes more mail toward spam folders, for everyone, not just the inactive subscribers.

There's also a slower risk: very old dormant addresses can be repurposed as spam traps. These are addresses that were once real but are now monitored specifically to catch senders with poor hygiene. Hitting even a few will damage your reputation quickly.

The practical response is setting a re-engagement threshold and acting on it. Most programs suppress or re-engage at 60 to 90 days of inactivity, depending on sending frequency. The faster you send, the shorter the window.

One word of caution: don't confuse decayed engagement with disinterest. Sometimes the content has drifted from what people signed up for, or the send frequency became too high. Before suppressing a large segment, check whether the decay is sudden (a quality issue) or gradual (natural churn).