In July of 2019, Microsoft will roll out a new feature in Teams (and if you aren’t using Teams… well, you’re missing out!) that will allow you to mark a message as priority. The priority mark will create periodic notifications for the recipient of your message to help ensure they see it.
From Microsoft themselves:
Microsoft Teams – Priority notifications
Share urgent messages and time-sensitive information more effectively with Teams. Priority notifications alert a recipient of an urgent message on their mobile and desktop devices until a response is received, every two minutes for up to 20 minutes. Note: For a limited time, unlimited Priority Notifications in Microsoft Teams will be made available for all customers. This promotion will run from July 2019 until December 31, 2019 and during this time all Teams users will be able to send unlimited Priority Notifications. Starting on January 1, 2020, licensed users will be able to send Priority Notifications according to the terms of their subscription. IT Admins will be given reporting on priority notification usage to support appropriate user licensing.