Send a Test Marketing Email

**This endpoint allows you to send a test marketing email to a list of email addresses**. Before sending a marketing message, you can test it using this endpoint. You may specify up to **10 contacts** in the `emails` request body field. You must also specify a `template_id` and include either a `from_address` or `sender_id`. You can manage your templates with the [Twilio SendGrid App](https://mc.sendgrid.com/dynamic-templates) or the [Transactional Templates API](https://docs.sendgrid.com/ap...