When a new message is received in Teams, the user always get a notification and there is a pop-up message with preview. 

This can be turned off in two ways:

1. If the notifications needs to be turned off during the meetings only, the status should be changed to "Do not disturb" and then there will be no notifications/pop-up messages during the meetings.

2. You can turn off the notifications/preview from the settings in Teams app.

• Open Microsoft Teams desktop or web client.
• Click on the user icon, located in the right hands side of upper Teams bar.
• Then click Manage Account to open the Teams Settings.
• From the left hands side of the Settings dialog, select Notifications.
• Then click the Custom button and you can see the option to Turn off the notifications/preview. Please see the attached image.