> ## Documentation Index
> Fetch the complete documentation index at: https://docs.onemrr.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Email impact

> Whether your customer emails actually change what customers do, measured against a holdout group.

A customer who got an email and stayed might have stayed anyway. **Churn & retention → Email impact** tells the two apart by comparing each email with a **holdout group**: eligible customers left out at random, who would otherwise have got it.

![Email impact, with the totals and one email's outcomes numbered 1 and 2](https://mintcdn.com/one-mrr/r0eSCeyIYQOzU0L6/images/churn/impact.png?fit=max\&auto=format\&n=r0eSCeyIYQOzU0L6\&q=85\&s=6b0a1bc3853197596fe9a0db9798385c)

## Choose the period

* **Decided in:** emails sent, or held back, in the last 90 days, 180 days or year.
* **Outcome measured after:** how long after each email to look at what the customer did: 30, 60 or 90 days.

## The totals

* **Emails sent** and replies from customers.
* **Held back:** customers in the holdout group.
* **MRR saved by email:** the difference between the emailed and held-back groups' saved rates, times the MRR of the emailed customers. It's counted only when the difference is clear at 95% confidence, and shows "—" until then.

## Each email

For **Before it ends**, **Retention check-in** and **Cancellation feedback** separately:

* **What the email did:** sent, delivered, opened, clicked and replied (and, for feedback, survey answered). Delivery and opens come from Postmark's reports; test emails never count.
* **What customers did:** for the emailed and held-back groups, who kept their plan, reactivated, is still paying, or churned, and the share saved. Customers still within the measurement window show as in progress.

Without a holdout group, OneMRR shows the emailed group's outcomes but says they might have stayed anyway. To measure properly, hold back a share of customers for each email in [Automations](https://docs.onemrr.dev/churn/automations.md).

## Not emailed any more

People who unsubscribed, whose address bounced, or who marked an email as spam. OneMRR checks this list before every customer email.


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