Some ASUS and compatible notebooks support an LED which should turn on when there are unread e-mails in the inbox. Unfortunately this only works with Microsoft Outlook® and the supplied Generic ChkMail driver.
ledBirdXP checks the registry-variable UnreadMail to control the LED using the ASUS driver if there are unread e-mails.
So it is independent from the used e-mail-client and works with other clients like Thunderbird from mozilla.org.