# onNew

Sets up a listener for the event when a new mail is sent.

### Usage

```ts
const receiver = '0x...';
const sender = '0x...';

// Listen to received mails
mail.onNew(null, receiver, (envelope) => {
  console.log(envelope);
});

// Listen to sent mails
mail.onNew(sender, null, (envelope) => {
  console.log(envelope);
});

// Listen to all mails
mail.onNew(null, null, (envelope) => {
  console.log(envelope);
});
```

#### Stop watching

```ts
// Listen to received mails
const stopWatching = mail.onNew(null, receiver, (envelope) => {
  console.log(envelope);
});

// ... Later, to stop watching for the events
stopWatching();
```

### Returns

`UnwatchFn`

A function that can be invoked to stop watching for new event logs.

### Parameters

#### sender

* **Type** `Address | null`

The mail sender's address. If set to null, it listens for mails from any sender.

#### receiver

* **Type** `Address | null`

The mail receiver's address. If set to null, it listens for mails to any receiver.

#### callback

* **Type** `(envelope: ReceivedEnvelope) => void`

The callback function to be executed when a new mail event is detected. It receives a ReceivedEnvelope as its only argument.