Some (but not all) people who send mail to our exchange
2000 server receive the error below:

----- The following addresses had permanent fatal errors -
---- <JOECOOL@xxxxyz.com>
(reason: 500 5.3.3 Unrecognized command)

----- Transcript of session follows -----
.... while talking to xxx.xyz.com.:
>>> DATA

<<< 500 5.3.3 Unrecognized command
554 5.5.0 Remote protocol error