From the groups memberhsip list in the User CP:
Usenet Membership. If you wish to post to usenet sections of the forum you need to join this group. Users who use free email addresses (yahoo etc.) or have an email address which doesn't match their ISP will not be able to join. Approvals take upto 24hrs
a lot of those USENET dudes like to fantasize that their "chatroom" is way more sophisticated, pure and highbrow than a lowly forum , so they don't want any old scallywags joining