What’s the difference between global frequency cap and per-segment cap?
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You've got two campaigns going out this week. A promotional blast. An automated flow. A newsletter. Before you know it, one subscriber got six emails in five days. That's where frequency caps come in. But not all caps work the same way.
A global frequency cap puts a ceiling on the total number of emails any one subscriber can receive across all your sends in a given period. Set it to three emails per week and it doesn't matter how many campaigns are queued up. Once that person hits three, they get nothing else until the window resets. It's a blunt instrument, but a useful one.
A per-segment cap works at a more granular level. Instead of limiting total emails, it limits emails within a specific category or stream. You might cap promotional emails at two per week while letting transactional and onboarding flows send freely. A subscriber could still receive five emails in a week if they hit different streams.
Here's the core trade-off. A global cap is easier to implement and protects everyone from over-mailing regardless of how complex your sending calendar gets. But it's not smart about which emails matter most. If a subscriber hits the global cap because of three promotional emails and then you send a shipping update, that update might get suppressed. That's a problem.
Per-segment caps give you more control. You protect high-value streams (transactional, onboarding, re-engagement) from being crowded out by promotional volume. The downside is you need to properly categorize every campaign and flow, and you need an ESP that actually supports this level of logic. Braze, Iterable, and Customer.io handle per-segment capping natively. Most simpler tools only offer global caps, if they offer capping at all.
Still the most practical approach for most senders is to use both together. Set a global cap as a safety net, then use per-segment caps to protect your most important flows. Think of the global cap as the outer boundary and the per-segment caps as the rules within it.
If you're working out each subscriber's ideal cadence, frequency caps are the enforcement layer that makes that strategy hold up even when your sending calendar gets messy.
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