curl --request GET \
  --url https://api.sendpost.io/api/v1/account/message/{message_id} \
  --header 'X-Account-ApiKey: <api-key>'

{
  "id": "4d9c5148-63fc-4999-99ea-fc997b0a24e2",
  "submittedAt": 1588760624008835300,
  "from": {
    "name": "PiedPipers",
    "email": "team@piedpiper.com"
  },
  "replyTo": {
    "name": "PiedPipers",
    "email": "team@piedpiper.com"
  },
  "to": [
    {
      "name": "Peter Gregory",
      "email": "peter@hooli.com",
      "customFields": "{\"Company\": \"Hooli\"}"
    }
  ],
  "headers": "{\"X-Campaign-Id\": \"User onboarding\"}",
  "subject": "Welcome to Pied Piper :) + 1 quick question",
  "preText": "Congrats and get some Pied Piper cred inside",
  "htmlBody": "Thanks for joining Pied Piper {{.FirstName}}.Pied Piper has changed many landscapes. Compression. Data. The Internet",
  "textBody": "Thanks for joining Pied Piper {{.FirstName}}.Pied Piper has changed many landscapes. Compression. Data. The Internet",
  "ippool": "transactional-piedpiper",
  "trackOpens": true,
  "trackClicks": true
}