effective internal email distribution lists

I've been thinking about internal e-communications within groups, and how much the dynamics change when more people are added.

The obvious way to deal with this is to split up the list along functional lines. For instance on a software project, having 4 lists: team-all, team-sales, team-qa, team-dev.

While this is useful, I think another important division is to differentiate between announcements and discussions. In fact, the internet community has a long-standing tradition of splitting SIG lists this way.

Key characteristics of discussion lists:

1. participation is optional
   
2. participation level is configurable
   
3. the discussion threads are archived
   

The configurable participation level allows users to decide how often they receive messages:

individually as they come in

batched together in a [daily] "digest" (or weekly, etc.)

some list-management software allows further tuning of digests, such as trimming the posts to just the first few lines
The online archive gives other benefits:

since you can read them on the web, it allows you the option of deleting them from your inbox

the web archive can be searchable via a search engine

some list-archiving servers act as online forums/bulletin-boards by providing an interactive messaging interface, thus allowing messages to be posted from the website to the list.

This last point is a gray area, since it is a convergence of newgroups with listserv.
The SocialText wiki engine can be made to simulate this through its email notifications.
SocialText email-and-forum-related features:

users can configure their workspace-wide notification interval between 5 minutes and 1 week.

users can click on "watch this page" which sends them an email when that page is modified.

an incoming email address posts messages to the wiki; the subject-line is the page title

each page has an "add comment" link on it