Frequency Caps: How Many Emails Before Subscribers Tune Out

There is a number of emails per week past which opens fall, complaints rise, and unsubscribes spike. Every store has one, and almost none of them know what it is.

Most stores hit the wall between three and five promotional emails a week, but the real cap is per subscriber, not per store. The fix is a cap in the sending platform, a separate cap for promotional mail, and a test that finds the number instead of guessing it.

The wall is real and measurable

Send one promotional email a week and opens hold steady. Send three and opens per email start to fall. Send five and the unsubscribe rate climbs, spam complaints appear, and the open rate on the emails that matter, order confirmations and shipping updates, starts to drop too. The subscriber is not angry. They are trained. Every extra email teaches them that the store's mail is skippable, and the lesson applies to all of it.

The damage is not linear. The first extra email costs little. The third costs more than the first two combined, because it is the one that pushes the subscriber from ignoring to unsubscribing. And the unsubscribe is permanent in a way the ignored email is not. A store that sends five emails a week to win one extra sale is trading a permanent subscriber for a single order.

Related reading on this site: PrefEngine and Preference Centers: The Five Questions Worth Asking (and the Rest to Drop) cover the neighbouring problems in more depth.

Caps per subscriber, not per store

A store-wide cap of three emails a week is the wrong tool, because subscribers are not the same. A new subscriber in their first week wants more mail, not less: the welcome flow, the first-purchase nudge, the category guide. A subscriber who has not opened in ninety days wants almost none. A single cap treats them identically and fails both.

The fix is a cap per subscriber segment. New subscribers get the welcome flow uncapped for two weeks, then join the standard cap. Engaged buyers get three promotional emails a week. Dormant subscribers get one a month, or none until they re-engage. Transactional mail, order confirmations and shipping updates, sits outside the cap entirely, because nobody unsubscribes over a shipping notification.

How to find your number

Run a holdout test. Split the list in half, cap one half at two promotional emails a week and the other at four, and watch for four weeks. Compare revenue per subscriber, not open rate, because opens are easy to game and revenue is not. If the four-email group earns more per subscriber with no rise in unsubscribes, the cap is higher than two. If it earns the same with more unsubscribes, the extra emails are pure cost.

Repeat the test quarterly. The cap moves with the seasons, the catalog, and the list itself. A store that found its number last year and never retested is sending on a guess. The test takes a month and the answer is worth a year of sends.

Frequently asked questions

How many promotional emails per week is too many?

Most stores hit the wall between three and five a week, but the real cap is per subscriber. Test it with a holdout rather than guessing.

Should transactional emails count toward a frequency cap?

No. Order confirmations and shipping updates sit outside the cap, because nobody unsubscribes over a shipping notification. Cap promotional mail only.

How do I test my email frequency cap?

Split the list in half, cap one half at two promotional emails a week and the other at four, and compare revenue per subscriber over four weeks.

Do new subscribers need a different frequency cap?

Yes. New subscribers in their first two weeks want more mail, the welcome flow and first-purchase nudges, while dormant subscribers want almost none. Cap per segment, not per store.