Message Not Delivered: Messaging command in transmission too long
The message could not be delivered becasuse mailing protocol parameters were not met as the commands used in message transmission were too long.
Try sending the message again in a while as this problem might be temporary or already in the process of being fixed.
If this error persists, contact the email provider for help.
5.5.6: Official Definition
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.
This enhanced status code SHOULD be returned when the server fails the AUTH command due to the client sending a [BASE64] response which is longer than the maximum buffer size available for the currently selected SASL mechanism. This is useful for both permanent and persistent transient errors.