Unfortunately I don't think the Webmail server knows how to speak NNTP although it's a good feature request.
If you want to have the webmail interface send mail to groups you control you could create a mailing list for that group that forwards the message to a NNTP gateway or invokes a program to deliver the message to the appropriate newsgroup.
I remember the old Netscape Collabra Server shipping with such a program that could be integrated into the old Netscape 3.6 Messaging Server so in theory it is possible.
I hope this helps some.
-Chris
It would likely depend on what your NTTP server is and what features it has. Collabra News Server had a feature called the <i>newsgateway</i> which allowed users to send messages through an address which was configured to interact with the Collabra(NNTP) server.
If I recall, this was entirely an NNTP feature and had little or nothing to do with configurations on the messaging server itself.
If your NNTP server offers a similar type of 'gateway' you could probably accomplish the same by adding some functions to the webmail code that would allow the user to send to the appropriate address (filling in the correct header information, etc) when they click on a button.
This would be a total hack and I have no knowledge of precedence for this.