How Exchange 2010 Uses Site Membership

How Exchange 2010 Uses Site Membership

Exchange 2010 is a site-aware application. Site-aware applications can determine their own Active Directory site membership and the Active Directory site membership of other servers by querying Active Directory. Exchange 2010 uses site membership to determine which domain controllers and global catalogs servers to use for processing Active Directory queries. Additionally, when an Exchange server has to determine the Active Directory site membership of another Exchange server, it can query Active Directory to retrieve the site name.

In Exchange 2010, the Microsoft Exchange Active Directory Topology service is responsible for updating the site attribute of the Exchange server object. Because the Active Directory site membership is a server object attribute, Exchange does not have to query DNS to resolve a server address to a subnet that is associated with an Active Directory site. Stamping the Active Directory site attribute on an Exchange server object also enables Active Directory site membership to be assigned to a server that is not a domain member, such as a subscribed Edge Transport server.

The Exchange 2010 server roles use Active Directory site membership information as follows:

• Mail submission The Mailbox server role uses Active Directory site membership information to determine which Hub Transport servers are located in the same Active Directory site as the Mailbox servers with the same server version. The Mailbox server submits messages for routing and transport to a Hub Transport server that has the same Active Directory site membership and the same server version as the Mailbox server.
  (P.S. 郵件提交的判斷條件: 先送往相同AD Site 及相同Exchange 版本的 Hub Transport Server)
  
  
• Mail delivery The Hub Transport server performs recipient resolution and queries Active Directory to match an e-mail address to a recipient account. The recipient account information includes the FQDN of the user’s Mailbox server. Hub Transport server queries the Active Directory to determine the Active Directory site of the user's Mailbox server. If the Mailbox server is in the same site as the Hub Transport server, it will deliver the message to that Mailbox server. Otherwise, it will relay the message to another Hub Transport server in the same site as the target Mailbox server for delivery. (P.S. 郵件傳遞的判斷條件: 先送往相同AD Site 及 相同Exchange 版本的 Hub Transport Server)
  

• Message routing Exchange 2010 Hub Transport servers retrieve information from Active Directory to determine how mail should be routed inside the organization.
  (P.S. 郵件路徑的判斷條件: 先送往相同AD Site 及 相同Exchange 版本的 Hub Transport Server)
  
  When a message is submitted to the Microsoft Exchange Transport service, the categorizer uses the header information in the message to query Active Directory for information about where the message must be delivered.
  1. If the recipient's mailbox is located on a Mailbox server in the same Active Directory site as the Hub Transport server and the version of the Mailbox server matches the Hub Transport server, the message is delivered directly to that mailbox.
  2. If the recipient's mailbox is located on a Mailbox server that has a different server version than the Hub Transport server, the message is relayed to a Hub Transport server in the site that matches the version of the Mailbox server. 
  3. If the recipient's mailbox is located on a Mailbox server in a different Active Directory site, the message is relayed to a Hub Transport server in that site and then delivered to the Mailbox server.
  
• Unified Messaging message submission
  The UM server role uses Active Directory site membership information to determine which Hub Transport servers are located in the same Active Directory site as the UM server. The UM server submits messages for routing to a Hub Transport server within the same Active Directory site. The Hub Transport server performs recipient resolution and queries Active Directory to match a telephone number, or other UM property, to a recipient account. Once the recipient resolution completes, the Hub transport server will deliver the message to the target mailbox in the same way as a regular e-mail message.
  (P.S. UM message 也是透過HUB 轉送，判斷收件者的電話、UM屬性所對應的account 後在傳送 )
  
  
• Client connections to CAS
  When the CAS server receives a user connection request, it queries Active Directory to determine which Mailbox server is hosting the user's mailbox. The Client Access server then retrieves the Active Directory site membership of that Mailbox server. If the CAS server that received the initial user connection is not located in the same site as the user's Mailbox server, the connection is redirected to a CAS server in the same site as the Mailbox server.
  (P.S. CAS 也是透過AD 查詢連線使用者的Mailbox 所在server，若不同AD Site，會重導至另一個AD 的CAS Server 上)
  
  
• Public Folder referrals
  Active Directory site membership and IP site link information is used to prioritize the list of servers that are used for public folder referrals. Users are directed first to the default public folder database for their mailbox database. If a replica of the public folder being accessed does not exist in the default public folder database, the Mailbox store where the default public folder database resides will provide a prioritized referral list of Mailbox servers that hold a replica to the client. Public folder databases that are in the same Active Directory site as the default public folder database are listed first, and additional referral locations are prioritized based on Active Directory site proximity. Active Directory site proximity is determined by aggregating the costs of the IP site links between the Active Directory site where the default public folder database resides and the Active Directory sites where public folder replicas exist. The list of referrals is prioritized from lowest cost to highest cost. The connecting client will try each referral in the list until a connection is made or all attempts fail.
  
  

More Information 
Planning to Use Active Directory Sites for Routing Mail