No `SuppressSending` key on the ESP event from Postmark

[dshunfen]

Hi, when an "unsubscribed" event is received by the Postmark webhook receiver, it appears there is a key check that checks for a potentially missing key here:

        if event_type == EventType.UNSUBSCRIBED:
            if esp_event["SuppressSending"]:

In my esp_event payload, the SuppressSending key does not exist:

{
  Description: "Unsubscribe or Remove request.",
  ID: 555555555,  # scrubbed
  MessageID: "5555555-5555555-5555-5555555",  # scrubbed
  MessageStream: "outbound",
  Name: "Unsubscribe request",
  RecordType: "Bounce",
  ServerID: 111111111, # scrubbed
  Tag: "",
  Type: "Unsubscribe",
  TypeCode: 16
}

Should this be an in check rather than a key assertion check?

[medmunds]

Thanks for the report, and for including the webhook payload example. (Postmark's webhook documentation tends to be incomplete, and in some cases just outright wrong.)

Should this be an in check rather than a key assertion check?

Almost. I think the right test is if esp_event.get("SuppressSending", True):—if the SuppressSending key is missing, treat it as unsubscribe. (This code handles both Postmark's "ManualSuppression" and "Unsubscribe" events, and we don't want to accidentally convert UNSUBSCRIBED to SUBSCRIBED.)

PR welcome if you're up for it.