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Segmentation isn't just a personalization tactic — it's a deliverability tactic. Sending relevant email to the right slice of your list keeps opens and clicks high and complaints low, which is exactly what inbox providers reward with primary-tab placement.
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Every send to your full, unfiltered list drags your engagement rate toward whatever your least-engaged subscribers do — which is usually nothing. Segmentation stops that. Instead of one send to everyone, you send the right message to the right slice, so aggregate engagement stays high and your sender reputation stays protected.
| Segment | Definition |
|---|---|
| Highly engaged | Opened or clicked in the last 30 days |
| Engaged | Opened or clicked in the last 60-90 days |
| At risk | 90-180 days without opening or clicking |
| Unengaged / sunset candidate | 180+ days without opening or clicking |
The 70/20/10 sending rule: send roughly 70% of your campaigns to your engaged segment only, 20% to a broader but still reasonably active audience, and 10% to the full list (reserved for genuinely important sends). This keeps your aggregate engagement rate high without starving your least-active-but-still-valid subscribers of every message.
RFM scores every customer on three dimensions from their purchase history — how recently they bought, how often, and how much they've spent. Most ESPs (Klaviyo included) calculate this automatically. Typical RFM segments: