At the start of June Microsoft announced Priority Notifications as a new addition to the Teams feature set.
Priority Notifications allow a user to mark a chat message in Teams as “Urgent”. Unlike regular “important” messages, Urgent Messages (aka “priority notifications”) notify users repeatedly for a period of 20 minutes or until messages are picked up and read by the recipient, maximizing the likelihood that the message is picked up and acted upon in a timely manner.
Admins can manage this feature as part of their messaging policies within Teams. This feature is on by default for all tenants. However, due to configuration issues, in some cases, if an admin has created a TeamsMessagingPolicy in the last 6 months, this setting might have been defaulted to OFF. In that case, tenants admins will have to set it back to ON explicitly.
One thing to note is that under the roadmap article 51448 it states: 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
In order for your users to send more than 5 urgent messages (which may be business critical) per month you will need to invest in a higher tier license.
For further information on managing messaging policies within Teams head over to HERE.