If your team is careful about only posting important announcements in the category, you could configure the category so that all users are watching the first post in all of the category’s topics. That would cause either an onsite notification or an email to be triggered for each new topic in the category. Some additional details about this are here: Send a personal message or email to all users on a Discourse site.
If you don’t want to risk annoying your users with too many emails or notifications, a dismissible banner topic could be useful for some announcements: Create a banner to display at the top of your site. The only downside of this is that the banner will only be seen by users who visit the site.
Discourse also allows you to “pin” a topic either at the top of a category’s topic list, or globally at the top of all topic lists. Pinned topics are created in the same way as banners - by clicking the “Pin Topic” entry from a topic’s actions menu.
For important messages that need to be seen by all users who visit the site, you can use the global notice site setting to create a non-dismissible global banner notice. These notices are normally used for urgent communication related to the site. For example, letting users know that the site will be going into read-only mode for a period of time.
Discourse recently released a Newsletter plugin: Discourse Newsletter Integration. I haven’t tried it yet, but this could be a great way of communicating with a site’s users. Possible downsides are that it requires having a Mailchimp account and that users need to opt in to receive the newsletter. I believe that for sites that are hosted by Discourse, this plugin is currently only available on Enterprise plans.