Use the following select statement: toRecipients

Example: GET https://graph.microsoft.com/v1.0/me/messages//?$select=subject,from,receivedDateTime,toRecipients

Response:

[{
  "receivedDateTime": "2024-12-04T01:32:05Z",
  "subject": "Undeliverable: XYZ",
  "bodyPreview": "Your message to [email protected] couldn't be delivered.....",
  "from": {
    "emailAddress": {
      "name": "Microsoft Outlook",
      "address": "[email protected]"
    }
  },
  "toRecipients": [
    {
      "emailAddress": {
        "name": "XYZ",
        "address": "[email protected]"
      }
    }
  ]
}]

For NDRs, you can then evaluate the toRecipients property - this contains the original destination address for NDRs.