Delayed Message: Email system sent bad command
The email message has not yet been delivered because the sender's email provider used a messaging command that the recipient's email provider didn't recognize.
Retry the email message see if it was a one-time problem or if the same error occurs.
Otherwise, contact the support team as the sender's mail system issued a command that is not supported by the recipient's email provider. This typically requires helpdesk support.
4.5.4: 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 valid mail transaction protocol command was issued with invalid arguments, either because the arguments were out of range or represented unrecognized features. This is useful only as a permanent error.