The title says it all. I want to be notified in the tray.
Click on Mail Watcher, and then on Add, and Close
Once done you'll see the icon on the panel.
Once done, right click on the icon, and choose properties, to be able to setup emails.
If you are using Thunderbird, then there is the Firetray extension.
When there's no unread email, it show the faded envelope icon (that can be configured otherwise). When there are unread emails, it shows their count.