You can keep track of how many emails you have that are unread in your inbox even when Mailbird is minimized. To show the unread email counter in the taskbar and system tray:
1) Go to the Mailbird menu in the top left of the main window.
2) Select "Settings"
3) Click the "General" tab
4) Check or un-check "Notifications: Show unread count in taskbar & system tray"
You can see the unread email count in the taskbar.
In the system tray if you have an unread email you will see a blue dot on the Mailbird icon