When you have an unread message from someone in a chat conversation, a red icon with the number of unread messages appears to the right of the contact’s name in the conversation pane.
Unread Group messages are indicated with a red outline.
Additionally, a badge appears next to your system tray icon that displays the number of unread messages.
Depending on your notification settings, a pop-up notification may also appear when an incoming message is received, as shown below.
Click the notification or contact or group’s name to navigate to the conversation and view the unread message.