Supercharge the Mail.app dock icon with DockStar
DockStar is an add-on for Mail.app that adds up to 5 new-mail indicators to the dock icon. This lets Mail users keep track of email as it arrives in various accounts and local mailboxes. In addition, DockStar brings customizable shapes and colors to the Mail dock icon. Seamless integration allows users to control every aspect of the dock icon directly from Mail's settings panel. It's an ideal addition for people with multiple e-mail accounts.