curl --request GET \
  --url https://api.railmail.app/api/v1/campaigns/{campaignKey}/report/statistics \
  --header 'X-API-Key: <api-key>'

{
  "campaignId": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "status": "<string>",
  "totalSent": 123,
  "totalDelivered": 123,
  "totalBounced": 123,
  "hardBounced": 123,
  "softBounced": 123,
  "totalOpened": 123,
  "uniqueOpens": 123,
  "totalClicked": 123,
  "uniqueClicks": 123,
  "totalUnsubscribed": 123,
  "spamComplaints": 123,
  "deliveryRate": 123,
  "openRate": 123,
  "clickThroughRate": 123,
  "clickToOpenRate": 123,
  "unsubscribeRate": 123,
  "bounceRate": 123,
  "engagementScore": 123,
  "collectedAt": "2023-11-07T05:31:56Z",
  "lastUpdatedAt": "2023-11-07T05:31:56Z",
  "completedAt": "2023-11-07T05:31:56Z"
}