> For the complete documentation index, see [llms.txt](https://docs.mailtrap.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.mailtrap.io/email-sandbox/testing/bounce-rate.md).

# Bounce Emulator

## Constructing the address

The recipient's username should start with bounce+ and contain the response in URL-encoded form: `bounce+550+no+such+user+here@inbox.mailtrap.io` .

To create it, use [https://www.urlencoder.org](https://www.urlencoder.org/) or any other URL encoding solution.

Tip: You cannot use capital letters because email addresses are converted to lowercase by any responsible SMTP client. But you can use URL encoding to express capital letters: `bounce+550+%4Eo+such+user+here@inbox.mailtrap.io` .

## Using Bounce Emulator with an email client

Just use the inbox.mailtrap.io host with any email client or application and send an email to `bounce+451+server+unavailable@inbox.mailtrap.io` .

## Using Bounce Emulator with Sandbox

If your application is connected to Email Sandbox SMTP, send an email from the application to `bounce+454+authentication+required@anydomain.com` , and your application will receive a bounce response from the Sandbox SMTP server.

*Note: This feature does not work with API, as bounce codes are specific to SMTP.*


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# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://docs.mailtrap.io/email-sandbox/testing/bounce-rate.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

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Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.