curl "https://api.v2.dealmachine.com/v1/mail/analytics/summary?start_date=2026-05-01&end_date=2026-05-31" \
  -H "Authorization: Bearer dm_sk_live_xxx"

{
  "data": {
    "summary": {
      "total_sent": 1240,
      "total_delivered": 1180,
      "total_failed": 22,
      "total_opened": 410,
      "unique_openers": 295,
      "avg_open_rate": 0.238,
      "campaign_count": 6
    },
    "campaigns": [
      {
        "campaign_id": "a1b2c3d4",
        "campaign_name": "Spring Seller Campaign",
        "status": "Completed",
        "total_sent": 300,
        "total_delivered": 286,
        "total_failed": 5,
        "total_opened": 96,
        "unique_openers": 71,
        "open_rate": 0.237,
        "created_at": "2026-05-01T14:30:00.000Z",
        "launched_at": "2026-05-02T09:00:00.000Z"
      }
    ]
  },
  "pagination": {
    "page": 1,
    "per_page": 25,
    "total": 6,
    "has_more": false
  }
}