Lookup for "500 2.6.2"
This status code indicates a successful delivery or other operation. Any details are simply notes.
Basic Status Code Details (500)
Syntax error, command unrecognized [This may include errors such as command line too long]
Enhanced Status Code Details (2.6.2)
Conversion required and prohibited
The content of the message must be converted before it can be delivered and such conversion is not permitted. Such prohibitions may be the expression of the sender in the message itself or the policy of the sending host.