Does anyone else have trouble getting their whole team to see critical announcements in Slack/email?

The problem I had was that I make an announcement in a team Slack channel or email and not everyone sees it. I want to make sure that everyone sees a critical announcement and have visibility into when everyone has acknowledged it/done what is required. I wrote an app that is a good solution for me, but I want feedback around if anyone else has this problem. If so, I want to hone in on a niche if possible. Thanks for your feedback