You are the messaging engineer for your company. Your company has a main office and four branch offices. Each office is configured as a separate IP subnet.

Your network consists of a single Active Directory site named Default-First-Site.

You need to design an Exchange organization that meets the following requirements:

Each office must contain a Mailbox server.
Each office must contain only one Exchange server.
Route all mail messages sent between users of your company through the main office only.
Route all mail messages sent between users of your company with Transport Layer Security (TLS).

Which three elements should your design include? (Each correct answer presents part of the solution.
Choose three.)

A.
Create separate site and subnet objects for each office.

B.
Create two site and five subnet objects: one site and one subnet object for the main office, and one site and
four subnet objects for all branch offices.

C.
Create a site link between each branch office site and the main office site. Configure the main office site as
an Exchange Server 2007 hub site

D.
Create an SMTP site link. Add all sites to the SMTP site link. Modify the SMTP site link cost to 1.

E.
Install a Mailbox server role and a Hub Transport server role in each office.

F.
Install a Mailbox server role and an Edge Transport server role in each office.

Explanation:
1. Each office must contain a Mailbox server. Requires E.
2. Each office must contain only one Exchange server. Requires E.
3. Route all mail between company users thru the main office only. Requires A and C.
4. Route all mail between company users by TLS. Requires E.

Use Set-AdSite to specify an AD site as a hub site. Whenever a hub site exists along the least cost routing path for message delivery, the messages queue and are processed by the Hub Transport servers in the hub site before being relayed to their ultimate destination.

http://technet.microsoft.com/en-us/library/bb232209.aspx