Message Not Delivered: Email system sent bad command
The message could not be delivered because the sender's email provider used a messaging command that the recipient's email provider didn't recognize.
Fixes
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.
5.5.2: Official Definition
[RFC3463] (Standards Track) from the The Internet Engineering Task Force (IETF) definition for codes that start with 5.X.X:
A permanent failure is one which is not likely to be resolved by resending the message in the current form. Some change to the message or the destination must be made for successful delivery.
[RFC3463] (Standards Track) from the The Internet Engineering Task Force (IETF) definition for codes that end with X.5.2:
A mail transaction protocol command was issued which could not be interpreted, either because the syntax was wrong or the command is unrecognized. This is useful only as a permanent error.