Send email with design or HTML.

Example request

{
  "design": {
    "counters": {
      "u_row": 1,
      "u_column": 1,
      "u_content_text": 1
    },
    "body": {
      "rows": [
        {
          "cells": [
            1
          ],
          "columns": [
            {
              "contents": [
                {
                  "type": "text",
                  "values": {
                    "text": "Hello World"
                  }
                }
              ]
            }
          ]
        }
      ]
    }
  }
}