A mail box is an area that stores your unread and read email messages. Email software programs like Outlook Express that comes with the Internet Explorer software package have a mailbox included within them. Everytime you are connected to the Internet, Outlook Express loads up your new and old email messages. You can also find an online mailbox at free email address providers such as Hotmail and Yahoo. Even though these mailbox's are in the form of a web site page they still have the same facilities as a mailbox program such as Outlook Express.