Install cairo-dock-messaging-menu-plug-in by entering the following commands in the terminal:
sudo apt update sudo apt install cairo-dock-messaging-menu-plug-in
Description:
Messaging menu plug-in Cairo-dock
A collection of official plug-ins and applets for cairo-dock. . This provide a menu that notices you about new messages from Mail or Chat applications. It handles Evolution, Pidgin, Empathy, etc.
Homepage: http://www.glx-dock.org/
Version: 3.4.1-2build1
Section: universe/x11