Watcher email alert fails intermittently

[cglencr (Craig Glencross)]

I am using ES 7.4 and have created a Watcher with an email alert. It is scheduled to go off once a day.

Some days it works. Others it fails. And this is with no changes to ES or environment.

When I go to research why and perform Simulate on the Watcher execute will fail but force_execute will succeed. How is this possible?

Here is the error message:

"actions": [
  {
    "id": "send_email",
    "type": "email",
    "status": "failure",
    "error": {
      "root_cause": [
        {
          "type": "messaging_exception",
          "reason": "failed to send email with subject [Watcher Notification: SFTR Batch Job Status - Daily] via account [exchange_account]"
        }
      ],
      "type": "messaging_exception",
      "reason": "failed to send email with subject [Watcher Notification: SFTR Batch Job Status - Daily] via account [exchange_account]",
      "caused_by": {
        "type": "s_m_t_p_send_failed_exception",
        "reason": "530 5.7.1 Client was not authenticated\n"
      }
    }
  }
]

},