@EMHmark7 did you end up figuring out how you want to get this working?
In Discourse, one way to get at what you want is to create categories and to let members in the community “subscribe” to those categories by choosing the “watching” notification level. The Default categories watching or Default categories watching first post are handy for having an announcements category on your site, to reach out to everyone on your site.
I believe there are ways to manage the above based on group membership or some other criteria but I haven’t done it myself in a while - maybe somebody else has a recipe they can share.
Another approach is to PM the groups directly - if you send a PM to a handful of groups and the same member is in multiple groups there will not be any duplication.
But it does sound to me like you might be looking for a different tool, if what you want is not a forum or community that people log into to participate in discussions but rather a bunch of mailing lists that sends out email.
All of this can live in code outside Discourse, so you don’t have to install it. If you are using WordPress then you can get a bunch of this for free using GitHub - discourse/wp-discourse: WordPress plugin that lets you use Discourse as the community engine for a WordPress blog · GitHub, and then use another WordPress plugin to handle the mailing list part.