Delayed Message: Sender's address is written incorrectly
The email message has not yet been delivered because the sending address is not a valid email address.
Review the sender's email address to identify any misspellings or missing letters.
In the settings or options of the sender's email program or webmail service, ensure that your own email address is entered correctly.
4.1.7: 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.
The sender's address was syntactically invalid. This can apply to any field in the address.