John Mack wrote, in part:
> I would like to separate subscribers into 2 groups - those that receive the newsletter
> and advertisements ONLY and those that receive every message sent to the list
> (discussions, newsletter, and advertisements).
>
> I plan to add the following topics by defining them in the list header:
>
> * Topics= NEWS,ADV,DISCUSSION
> * Default-Topics= NEWS,ADV,OTHER

You might consider omission of the discussion topic, allowing "other" to
  be discussion.  Asking people to discuss stuff by always starting
their subject lines with "Discussion:" or "D:" will be very difficult,
unless there are very few discussionists.  So I would consider using..

* Topics= News,Adv
* Default-Topics= All

When you want someone to be in your news/adv-only group, you simply
remove "Other" as one of their topics.

The chances of someone beginning a subject line with "News:", with
ignorance of your topics is small, IMHO.

There is, however, a good chance of someone replying to one of your
"News:" postings using the same subject line ... and so now your
news-only subscribers are viewing discussion!  Since you cannot
authorize posting by topic, your only choice will be to intervene via
moderation.

cheers, wayne