Mailbox Server is a back-end server that hosts mailboxes, public folders, and their messaging data, such as address lists, and meeting items.
Client Access Server accepts Exchange Server connections from a variety of clients. This server hosts the protocols used by all clients when checking messages. On the local network, Microsoft Outlook MAPI clients are directly connected to the Client Access server to check mail. Remote users can check their mail over the Internet by using Outlook Anywhere, Outlook Web App, Exchange ActiveSync, POP3, or IMAP4,
Unified Messaging Server is a middle-tier server that connects a private branch exchange (PBX) system with ExchangeServer 2010, that allow voice messages and faxes to be stored with e-mail in a user's mailbox. It also supports call with automated greetings and message recording, fax receiving, and dial-in access. With dial-in access, users can use Outlook Voice Access to check voice mail, e-mail, and calendar information; to review or dial contacts; and to configure preferences and personal options.
Hub Transport Server is a mail routing server that handles mail flow, routing, and delivery within the Exchangeorganization. This server processes all mail that is sent inside or outside the organization. It also filter the contents. To meet any regulatory or organizational compliance requirements, the Hub Transport server can also record, or journal, messages and add disclaimers to them.
Edge Transport Server is an additional mail routing server that routes mail into and out of the Exchange organization. This server is designed to be deployed in an organization's perimeter network and is used to establish a secure boundary between the organization and the Internet. This server accepts mail from the Internet and from trusted servers in external organizations, processes the mail to protect against spam messages and viruses, and routes all accepted messages to aHub Transport server inside the organization.