# Scheduling Parameters

With scheduling, you can send large volumes of email in queued batches or target individual recipients by specifying a custom UNIX timestamp parameter.
Using the parameters defined below, you can queue batches of emails targeting individual recipients.

> \[!NOTE]
>
> **Emails can be scheduled up to 72 hours in advance.** However, this scheduling constraint does not apply to campaigns sent via [Marketing Campaigns](/docs/sendgrid/ui/sending-email/how-to-send-email-with-marketing-campaigns/).

This parameter allows SendGrid to begin processing a customer's email requests before sending. SendGrid queues the messages and releases them when the timestamp indicates. This technique allows for a more efficient way to distribute large email requests and can **improve overall mail delivery time** performance. This functionality:

* Improves efficiency of processing and distributing large volumes of email.
* Reduces email pre-processing time.
* Enables you to time email arrival to increase open rates.
* Is available for free to all SendGrid customers.

> \[!NOTE]
>
> Cancel Scheduled sends by including a batch ID with your send. For more information, check out [Cancel Scheduled Sends](/docs/sendgrid/api-reference/cancel-scheduled-sends/create-a-batch-id)!

When passing `send_at` or `send_each_at` please make sure to only use UNIX timestamps passed as integers, as shown in our examples. Any other type could result in unintended behavior.

> \[!CAUTION]
>
> Using both `send_at` and `send_each_at` is not valid. Setting both causes your request to be dropped.

## Send At

To schedule a send request for a large batch of emails, use the `send_at` parameter which will send all emails at approximately the same time. `send_at` is a [UNIX timestamp](https://en.wikipedia.org/wiki/Unix_time).

### Example of send\_at email header

```json
{
  "send_at": 1409348513
}
```

## Send Each At

To schedule a send request for individual recipients; use `send_each_at` to send emails to each recipient at the specified time. `send_each_at` is a sequence of UNIX timestamps, provided as an array. There must be one timestamp per email you wish to send.

### Example of send\_each\_at email header

```json
{
  "to": [
    "ben@example.com",
    "john@example.com",
    "mikeexampexample@example.com",
    "example@example.com",
    "example@example.com",
    "example@example.com"
  ],
  "send_each_at": [1409348513, 1409348514, 1409348515]
}
```

To allow for the cancellation of a scheduled send, you must include a `batch_id` with your send. To generate a valid `batch_id`, use the [batch id generation endpoint](/docs/sendgrid/api-reference/cancel-scheduled-sends/create-a-batch-id). A `batch_id` is valid for 10 days (864,000 seconds) after generation.

### Example of including a batch\_id

```json
{
  "to": [
    "ben@example.com",
    "john@example.com",
    "mikeexampexample@example.com",
    "example@example.com",
    "example@example.com",
    "example@example.com"
  ],
  "send_at": 1409348513,
  "batch_id": "MWQxZmIyODYtNjE1Ni0xMWU1LWI3ZTUtMDgwMDI3OGJkMmY2LWEzMmViMjYxMw"
}
```

## Additional Resources

* [SMTP Service Crash Course](https://sendgrid.com/blog/smtp-service-crash-course/)
* [Getting Started with the SMTP API](/docs/sendgrid/for-developers/sending-email/getting-started-smtp/)
* [Integrating with SMTP](/docs/sendgrid/for-developers/sending-email/integrating-with-the-smtp-api/)
* [Building an SMTP Email](/docs/sendgrid/for-developers/sending-email/building-an-x-smtpapi-header)