Lots of existing topics on this here, a quick search should bring them up.
In short, you have 3 options I can think of off the top of my head (I’d recommend #3):
- Mention all your users by username in the post. Not ideal, looks messy, and may require site setting changes based on the number of users you have.
- Mention
@trust_level_0
which will notify users TL0 and above (all users). May require a site setting change to increase max user notified per group mention. - Create a category which all users watch the first post of. You can use How do I set category tracking level defaults historically to change the user preference for all users to watch the first post of your new category.