Finding User Mailboxes

To provide access to mailbox folders through HTTP, you must have a virtual directory on both the Exchange front-end and back-end servers that points to the mailboxes.
Note:
User mailboxes cannot be stored on the front-end server.
When you install Exchange, a virtual directory named "Exchange" is created in the default virtual server. This directory points to the default SMTP domain for the Exchange organization. When you configure additional virtual directories on the front-end server through Exchange System Manager, you can select the SMTP domain name. In Exchange 2000 Server SP3 and Exchange Server 2003, users connecting to that virtual server must have an e-mail address in their list of SMTP proxy addresses on their object in Active Directory with the same domain. In Exchange Server 2003 SP1, users can override the SMTP domain by specifying the SMTP address in the URL (for explicit logon), or just use an implicit logon. For more information see "Logging on to Outlook Web Access" later in this topic.
In the dialog box where the SMTP domain is selected, the list of domains is a list of all domains for which there are recipient policies. Therefore, you might see duplicates in the list; it is not important which one you select.
When the front-end server detects a request to a location in the mailbox store (based on the setting of the virtual server or directory), it contacts an Active Directory global catalog server in the domain using Lightweight Directory Access Protocol (LDAP) and determines which back-end server contains the user's mailbox.