It works great as a newsletter. You only need to set some options.
Do not allow digest membership
Make sure admin must approve all postings.
To send your newsletter, you just send it from the admin email address you set, to the list. Then go into the panel and approve your 'post'.
It will mail out immediately, and there you have it.
The public sees it's signing up to a Newsletter, not a forum, so they don't even try to post. Also, if somebody who's savvy tries to post, you'll just get a notice from the list saying somebody tried to post. You can then go in and not approve their post, and even send them a courteous letter that this is not an open forum, it is just a newsletter, and they can send comments to the editor
Hope this helps.