A server role is a unit that logically groups required components and features that are needed to perform functions within a messaging environment. During installation, you choose the role(s) that the server will play within the organization. The following table describes the different types of roles in an Exchange 2007 environment:
Server Role
Description
Mailbox server
The Mailbox server role in Exchange 2007 contains the mailbox and public folder databases. Mailbox servers provide services such as:
Calculating e-mail address policies and address lists for recipients
Enforcing managed folders.
The Mailbox server interacts directly with the following:
Active Directory directory service server
Client Access server
Hub Transport server
Microsoft Outlook clients
Unified Messaging (UM) server
Client Access server
The Client Access server role allows a variety of different clients to communicate with the Exchange server. The Client Access server role hosts the following client applications and protocols:
Outlook Web Access
Exchange ActiveSync
Post Office Protocol version 3 (POP3)
Internet Message Access Protocol version 4rev1 (IMAP4)
You should know the following about Exchange protocols in relation to Client Access servers:
In previous versions of Exchange, the back-end server could be accessed using MAPI or any Internet protocol (POP3, HTTP, IMAP4). The only protocol used to communicate to a Mailbox server in Exchange 2007 is the MAPI RPC protocol.
In Exchange 2007, the Client Access server is responsible for all MAPI access. If a user wishes to use Outlook Web Access then they will use RPC/HTTP (Outlook Anywhere). If a user wishes to use POP3 or IMAP4, they will need to contact the Client Access server.
At least one Client Access server is required in every Exchange 2007 organization. In addition, each site that has a Mailbox server also requires a Client Access server.
Edge Transport server
The Edge Transport server handles all Internet-facing ingoing and outgoing mail flow and provides Simple Mail Transfer Protocol (SMTP) relay and smart host services for the Exchange 2007 organization. You should know the following about Edge Transport servers:
In past versions of Exchange, the Exchange server was a domain member but could still be face-to-face with the Internet. If the Exchange server were compromised, the entire domain could be compromised as well. For this reason, the Edge Transport server in Exchange 2007 does not require domain membership, but is designed to be deployed within a perimeter network.
The Edge Transport server does not have access to the Active Directory service, but instead runs a service called the Active Directory Application Mode (ADAM) which is a scaled-down, read-only version of Active Directory that can be deployed on a single machine, but does not require the DNS services and the supporting infrastructure that a full Active Directory implementation requires. The Edge Transport server stores all of its configuration in a local database.
Agents run on the Edge Transport server which provide protection against spam and viruses and apply rules to overall mail flow control.
It is possible to install more than one Edge Transport server in a perimeter network to provide redundancy in case of server failure.
The Edge Sync service makes it possible to set up Active Directory data synchronization between the Hub Transport server and the Edge Transport server. This allows the Hub Transport server to actually contact the Active Directory domain controller and global catalog server to retrieve information such as the recipients for the organization and the accepted domains and connectors, then it populates the information out to the ADAM instance on the Edge Transport server.
Hub Transport server
The Hub Transport server role is responsible for processing and delivering all messages within the Exchange Organization. The Hub Transport server role:
Is deployed inside the Active Directory service.
Is responsible for applying organizational policies.
Uses the store driver to:
Deliver mail to recipient's mailboxes within the organization.
Retrieve messages from a user's mailbox and place them in the Submission queue.
Determines the routing path for all messages in the organization and routes messages to recipient's mailboxes who reside outside of the organization.
Uses the categorizer feature to perform recipient resolution, content conversion, and routing resolution for all messages within the organization.
Unified Messaging server
Unified Messaging allows users to access e-mail, voicemail, calendar information, and fax communications using an e-mail client such as Microsoft Outlook, Outlook Web Access, or a mobile device that has Microsoft Exchange ActiveSync. The Unified Messaging server allows the Exchange organization to connect to a Private Branch eXchange (PBX) system.
Unified Messaging integrates voicemail, faxes, and calendars in the following ways:
All e-mail, voicemail, calendar, and fax communications are combined into a single store which is available from a telephone or computer.
All voicemails are converted to Windows Media audio files which are sent to the user's Mailbox server and stored as attachments in an e-mail.
When a fax is received, the fax can be converted into a .tif file which is saved as an attachment in a user's mailbox.
Users are provided with voice-based access to their mailbox through voice-prompts and queries. This allows users to perform the following tasks over the phone:
Access voicemail.
Listen to calendar information.
Listen, reply, or forward e-mail messages.
Access or dial contacts stored in the global address list or their personal contact list.
Accept or cancel meeting requests.
Set a voicemail out-of-office message.
Set personal options and security preferences.
The auto attendant feature allows external users to use the telephone keypad or speech inputs to navigate the Unified Messaging System to locate and/or call a user. It also allows the administrator to perform the following tasks:
Create a set of menus that can be customized for external users.
Define schedules for holidays.
Explain how to search the organization's directory to connect either directly or by using their extension.
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