qmail, port 587 only authenticated

[split]

Hi,

I want to use the TCP:587 port to authenticated email users. How to open this port is easy; just create a new file in xinetd.d with "service submission".

The problem is that I want that this port only accepts authenticated email.

Using this pluging for SPP:

http://xs3.b92.net/tomislavr/qmail.html

seems to work, but only "seems"
As I've read in other posts, SMTPAUTHUSER environment variable is not defined by Plesk's qmail so the plugin can't see wich is the authenticated user.

Any idea?
Thanks!