454 4.7.0 Temporary authentication failure

When an SMTP mail server responds to an attempted email delivery with the error message:

454 4.7.0 Temporary authentication failure
This indicates a temporary mail server system failure which prevented it from being able to verify the supplied authenticated credentials.

There's no need to correct the username and password in this case, but the user should be notified of the failure and email sending should be retried at a later time.