Multiple accounts are used to check for messages from more than one email address and/or mail server. Select → and click on the Accounts page to add or change your account settings. See the Getting started section for more information on the settings in the Accounts page.
To check for messages from a particular account, use the → submenu to select the account to check for mail. You can also press the mouse button on the Check Mail icon for some time to get a list of accounts.