Not only can you see how many new messages there are in your In folder, you can also make Mac OS X Mail fetch new mail from the server via its Dock icon.
Check for New Mail from the Mac OS X Mail Dock Icon
To check for new mail from the Mac OS X Mail Dock icon:
- Click on the Mac OS X Mail Dock icon with the right mouse button.
- Alternatively, click while holding down the Ctrl key or
- click and hold the mouse button until the menu comes up.
- Select Get New Mail from the menu.