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

# How to find customers with send failures or undeliveries

Customers may not receive a campaign if:

* **Failed to send from Maestra** (e.g., no subscription, expired consent, customer in Control Groups list, etc.);
* **Failed to deliver to the recipient's email server**.

Both types of events can be found in **campaign engagement tab**.
​

![](https://mintcdn.com/maestraio/8PhODeBuBM8nSWYH/images/imported/--2026-01-15--17_46_09.png?fit=max\&auto=format\&n=8PhODeBuBM8nSWYH\&q=85\&s=f6e818bffbc540c47217e793b011eab1)

You can also view the **error reason** and additional details there.

![](https://mintcdn.com/maestraio/8PhODeBuBM8nSWYH/images/imported/--2026-01-15--17_49_46.png?fit=max\&auto=format\&n=8PhODeBuBM8nSWYH\&q=85\&s=8850a1f25ec13ea72fdc0134fc5a3189)

Campaign engagements and customers can be **filtered by these reasons**.

* Find all undeliveries with the reason **Mailbox full**.

![](https://mintcdn.com/maestraio/O0b_zyYQP7Y48mll/images/imported/How-to-find-clicks-on-specific-links-in-campaigns-\(8\).png?fit=max\&auto=format\&n=O0b_zyYQP7Y48mll\&q=85\&s=81cee46c87d312ae561fbc2e30bd2bb1)

* Find all send failures where the message could not be composed.

![](https://mintcdn.com/maestraio/O0b_zyYQP7Y48mll/images/imported/How-to-find-customers-with-send-failures-or-undeliveries.png?fit=max\&auto=format\&n=O0b_zyYQP7Y48mll\&q=85\&s=36214decaf837bddd311e90911e0cd51)

* Find customers who had two or more undeliveries with the reason **Recipient rejected email due to content** for the last week.

![](https://mintcdn.com/maestraio/O0b_zyYQP7Y48mll/images/imported/How-to-find-customers-with-send-failures-or-undeliveries-\(1\).png?fit=max\&auto=format\&n=O0b_zyYQP7Y48mll\&q=85\&s=a5283a7d740bf81555bdd4dc91cf08fc)


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