Second, If you open chat conversations in separate top-level windows, you can prevent having multiple top-level windows from the same user or group. In Preferences, check Show single window for conversations with same user. This setting only applies when Show conversations in separate windows option is enabled, meaning chats are opened in a separate top-level window instead of shown in a panel of the main Skype for Business window. If both settings are enabled, and you have a chat window open with a user, any new messages from that user will be shown in the open chat window. This is true even if those messages show up in the Chats list as a separate session.