IF I send the command
newgroups 19700101 000000 GMT
I get the response
231 list of new newsgroups follows
503 program fault - command not performed System.ArgumentOutOfRangeException: Year, Month, and Day parameters describe an un-representable DateTime.
 
There are several problems here
1) The 4 digit year is valid - it was added in RFC 3977.
2) The error code should be 501 as it is an error parsing arguments.
3) Only the first line can be a response - strictly here the 503 is a group name and you MUST terminate the list with a period.
 
Additionally there is a very long pause after issuing the 231 response if there is no error parsing the arguments, once the 231 response is sent the server MUST provide a list of groups - there is no way to provide a second status code and the server MUST NOT close the connection without first issuing a 400 response to a command.