Delayed Message: User authentication for message failed
The email message has not yet been delivered because there was a problem with your user authentication to your email system.
Review the email account settings. Check for options that require "user authentication" for outbound SMTP and ensure that the Username and Password values are correct.
If the account settings are correct, contact the email provider to help identify any misconfiguration with the sender's account or with the email system.
4.7.4: Official Definition
A persistent transient failure is one in which the message as sent is valid, but persistence of some temporary condition has caused abandonment or delay of attempts to send the message. If this code accompanies a delivery failure report, sending in the future may be successful.
A message contained security features such as secure authentication that could not be supported on the delivery protocol. This is useful only as a permanent error.