The following will be replicated to AD LDS after configuring edge sync:

• A listing of all internally accepted domains
• A listing of all remote domains
• Any configured message classifications
• Information about internal send connectors that have been configured
• A listing of all valid internal SMTP addresses for the domain, which includes mailbox-enabled users, mail users, mail contacts, mail-enabled groups, and mailenabled public folders
• The safe and blocked sender lists that have been configured for each of these users.

The primary function of the Hub Transport server is to route messages for delivery within the Exchange organization. while messages are being routed through the Hub Transport server, we can apply transport rules and filtering policies that determine where they will wind up, such as in a compliance mailbox in addition to the recipient’s mailbox.

The Unified Messaging server role provides the following functionalities to an Exchange Server 2010 organization:

• Voice call answering, voicemail recording, and delivery o NN f voicemail to Exchange mailboxes.
• Voicemail access via a phone connection
• Voicemail preview
• Message read-back via a phone connection, including replying to the message or forwarding it to another recipient
• Calendar access via a phone connection, including meeting request acceptance
• Out-of-office messages in voicemail via a phone connection.

For the security purpose the Edge Transport server should be installed on out of internal network. Because The Edge Transport server is used to provide a secure SMTP gateway for incoming and outgoing messages of our organization. And its primarily responsible for antivirus and antispam controls as well as for protecting the recipient data held within Active Directory. Whenever an inbound message is received by the Edge Transport server, it scans the messages and then takes the appropriate actions if it determines that the message is a virus or if it appears to be a spam message.

Intersite Topology Generator (ISTG), which is responsible for the connections among the sites. By default Windows 2003 Forest level functionality has this role.
By Default the first Server has this role. If that server can no longer preform this role then the next server with the highest GUID then takes over the role of ISTG.