If you want to know which of your employees has already read your messages, you can easily find out.
Please log in to the portal (with appropriate rights for the messages).
Click on "Messages" in the main menu on the left
and select the desired message on the right of the main menu.
Now click on the item "Read".
Here you can now see who has already confirmed your message as read.
Regardless of the read confirmation, you can also see who opened this message and when.