Lookup for "500 4.6.0"
Temporary Error - This status code indicates a transient issue and may resolve itself.
Basic Status Code Details (500)
Syntax error, command unrecognized [This may include errors such as command line too long]
Enhanced Status Code Details (4.6.0)
Other or undefined media error
Something about the content of a message caused it to be considered undeliverable and the problem cannot be well expressed with any of the other provided detail codes.