OK, I recently needed to do a quick and dirty mail send from java using an exchange server. I kept getting a 501 5.5.4 error back, which is Invalid Arguments to the RSET method. It turns out, when looking at the example:
I had neglected to set the submitter properly. When googling, all of the discussions were around trailing dots or spaces. After wiresharking it, I finally saw the problem.
Word to the wise, make sure when you are using AUTH with SMTP to set the submitter properly.