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

# mailofly.dev Domain Error

> Understanding limitations and restrictions on the default test domain.

When testing Mailofly without adding a custom domain, you can send emails using the shared testing domain `onboarding@mailofly.dev` (or `test.mailofly.dev`).

If you encounter an error when sending via the test domain, review the constraints below.

## Common Reasons for Errors

### 1. Sending to Unverified External Addresses

The default test domain is strictly sandboxed. You can only send test emails to the **email address associated with your Mailofly account**.

If you attempt to send an email to any third-party recipient, the API returns:

```json theme={null}
{
  "statusCode": 403,
  "message": "You can only send to your own registered account email while using the test domain. Please add and verify a custom domain to send to external recipients."
}
```

### 2. Rate Limits on Shared Domains

Shared testing domains are subject to strict per-minute and per-day rate limits to protect reputation across all developing accounts.

## Solution: Add Your Custom Domain

To send to any recipient without sandboxing restrictions:

1. Navigate to **Domains** in your Mailofly dashboard.
2. Click **Add Domain** and enter your domain name (e.g. `yourcompany.com`).
3. Add the generated DKIM, SPF, and MX records to your DNS provider.
4. Once verified, update your `from` address to match your verified domain (e.g. `notifications@yourcompany.com`).


## Related topics

- [Errors](/api/errors.md)
- [Error 1010](/guides/domains/error-1010.md)
- [Domain already registered](/guides/domains/domain-already-registered.md)
- [Domain Mismatch](/guides/domains/domain-mismatch.md)
- [SDKs](/sdks/index.md)