Lookup for "500 4.7.9"
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 (4.7.9)
Authentication mechanism is too weak
The selected authentication mechanism is weaker than the server policy permits. Client should retry with a new authentication mechanism.