Gmail - Any way for us to know if an email we received bounced?

We have a google apps for work gmail that is not receiving an email from Zapier (routed through another two servers, one of which is mailgun, with a 605 error)

The difference between this one and the other is that we have checked our MX records (they are pointing to googles servers), google techs have helped us check this, but not able to offer an answer. Having followed up with three teams, I have come to stack for help.

Attached is the code.

    {
  "severity": "permanent",
  "tags": [],
  "delivery-status": {
    "message": null,
    "code": 605,
    "description": "Not delivering to previously bounced address",
    "session-seconds": 0
  },
  "envelope": {
    "targets": "radub@nwwpros.com",
    "transport": "smtp",
    "sender": "contact@zapier.com"
  },
  "recipient-domain": "nwwpros.com",
  "id": "Y0wp1sUWRs2aBtLZYJlvOg",
  "campaigns": [],
  "reason": "suppress-bounce",
  "user-variables": {},
  "flags": {
    "is-routed": null,
    "is-authenticated": true,
    "is-system-test": false,
    "is-test-mode": false
  },
  "log-level": "error",
  "timestamp": 1444147226.022885,
  "message": {
    "headers": {
      "to": "radub@nwwpros.com",
      "message-id": "20151006160014.2675.4025@zapier.com",
      "from": "Zapier <contact@zapier.com>",
      "subject": "[ALERT] Possible error on your \"Ask them how we did\" Zap!"
    },
    "attachments": [],
    "recipients": [
      "radub@nwwpros.com"
    ],
    "size": 42617
  },
  "recipient": "radub@nwwpros.com",
  "event": "failed"
}

Solution

I'm fairly certain Mailgun's 605 error code means Mailgun is blocking the message at their end, without even trying to send it to Google.

So there's nothing you could check in your Google Apps to find or fix the problem.

Mailgun's explanation (from your error) is "Not delivering to previously bounced address". That means your "to" address is in Mailgun's permanent block list for Zapier's Mailgun account, based on a past bounce. If your address is deliverable again now, Zapier could remove you from the Mailgun suppression list in the Mailgun dashboard under "Suppressions", or using Mailgun's bounce suppression API.