# E-mail check at sign-up

> Catch typos and missing mailboxes at sign-up with the MobileValidate e-mail check: fix invalid addresses, confirm unknown mailboxes and allow uncertain answers. Node and Python.

Canonical: https://mobilevalidate.com/docs/recipes/email-signup-check · Last updated: 2026-09-25

This recipe checks an e-mail address before you send the confirmation e-mail. It catches typos and mailboxes that don't exist, without blocking real users on uncertain answers. There is a [Node version and a Python version](https://github.com/brntech/mobilevalidate-sdk/tree/main/examples/email-signup-check).

## What does it decide?

| Result | Decision |
|---|---|
| `email_status` is not `valid` | Fix: show the API's `suggestion`, such as a mistyped domain |
| `registered: false` | Confirm: "We couldn't find this mailbox. Is the address spelled correctly?" |
| `registered: true` | Allow |
| `registered: null` (unknown) | Allow |
| The check fails | Allow, and log the error code and request id |

## What does the code look like?

```js
const { data, error } = await mv.lookup({ emails: [email], checks: ["email"], wait: 5, waitTimeoutMs: 8_000 });
if (error) return { decision: "allow" };                    // fail open
const row = data.results[0];
if (row.email_status !== "valid") return { decision: "fix", message: row.suggestion };
const registered = row.checks["email.valid"].registered;
if (registered === false) return { decision: "confirm" };
return { decision: "allow" };                               // true, or null (unknown)
```

```python
lookup = mv.lookup(emails=[email], checks=["email"], wait=5, wait_timeout=8)
row = lookup["results"][0]
registered = row.get("checks", {}).get("email.valid", {}).get("registered")  # True / False / None
```

## How do I test it?

Use the test addresses on `test.mobilevalidate.com` with the public sandbox key: `registered@` allows, `not-registered@` asks to confirm, `unknown@` allows and `pending@` allows after about 5 seconds. See [test values](/docs/test-values). Log the error code and `requestId`, never the address itself.

## Frequently asked questions

### Should I block sign-ups when the mailbox is not found?

No. Ask the user to confirm the spelling and let them continue if they insist. Block only addresses that are invalid.

### Does the e-mail check return names or profiles?

No. E-mail answers are yes, no or unknown only.