we are currently using notification service to receive notifications on our webhook. Today we send in the payload of email messages the "MessageKey" field as our unique identifier. However, in the email return events EmailOpen, EmailClick and EmailUnsubscribe we do not receive this field and therefore we cannot associate the event with our sent message. Would it be possible to put this field in the return of these events? How do the Sales Force customers identify and associate the sent with these status? Follow an example of Sent payload with the field "MessageKey" inside "info", we would like the same field on EmailOpen, EmailClick and EmailUnsubscribe.

    "eventCategoryType": "TransactionalSendEvents.EmailSent",
    "timestampUTC": 1600698608530,
    "compositeId": "466651f2-9c28-e911-a261-78e3b50b4f00.2001070.44609.4153.1251508322",
    "composite": {
        "jobId": "2001070",
        "batchId": "4153",
        "listId": "44609",
        "subscriberId": "1251508322",
        "emailId": "182583"
    "definitionKey": "makana-appt",
    "mid": 1447640,
    "eid": 1447640,
    "sendClassificationType": "Operational",
    "info": {
        "to": "[email protected]",
        "subscriberKey": "[email protected]",
        "messageKey": "f2b21aa0-fc16-11ea-9bc1-fbf804a5a66e",
        "status": "Sent",
        "renderedSubject": "Don't Forget Your Appointment"
    "definitionId": "466651f2-9c28-e911-a261-78e3b50b4f00"

1 Answer 1


Marketing Cloud-internally, the combination of jobId, listId, batchId and subscriberId constitutes a unique sendout event.

If your other events are returning those four (I am assuming, as I don't see them in your post and don't have examples at hand), you can use them to match to your sendout event, and thus your external messagekey.

In short: messageKey is defined externally (by you(r external system)) and matches 1:1 to the combination of jobid + listId + batchID + subscriberId which Marketing Cloud auto-generates at send time. Hope this helps :)

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