Both feeds and distribution lists are meant for top-down communications.
As far as distribution lists are concerned, you decide who the recipients are. You can add and remove Threema IDs to distribution lists at any time.
Feeds are similar to newsletters. Users can subscribe to and unsubscribe from feeds on their own. As Broadcast administrator, you can also subscribe and unsubscribe users from feeds. A feed’s blacklist allows to prevent certain users from subscribing to the feed.
Activate Availability: Internal only to prevent external users from subscribing to feeds.