A. The mailbox data is probably the most critical element of a messaging system because it's your content, but having the mailbox server on its own at a disaster recovery location isn't actually that helpful. There our other infrastructure services that will be key:

  • Domain Controllers—Authentication and directory service functions. Active Directory (AD) also acts as the configuration container for Exchange and is critical for failover clustering. These controllers must be running Windows Server 2003 SP1 or later and be writable domain controllers, not read-only.
  • DNS—Users and Exchange services need to be able to resolve names.
  • Hub Transport server—Any email is bounced off of a hub transport server, even if the recipient is on the same Exchange server as the sender.
  • Client Access Server (CAS)—Although MAPI clients in Exchange 2007 access the mailbox server directly via MAPI, you still need a CAS in each site with a mailbox server. The CAS provides not only OWA and ActiveSync connectivity, but also the availability service for calendaring and free/busy and the AutoDiscover function.
  • Anti-virus software installed on all roles matching primary site anti-virus deployment.

The services above are the minimum, must-have services. There are others that you may need or want depending on your configuration.

  • Edge server role—In your DMZ network to receive incoming traffic.
  • MX record with entry to the second site, if the primary site received email and the secondary site now needs to receive mail from the outside world.
  • Firewall services in the DMZ.
  • Unified Communications server, if used.
  • Backup services such as DPM—This will depend on how long you will be using the DR site. It could be for a while, necessitating backups.
  • Fax/BlackBerry/Voicemail integration components.

There may be other services at your location, but the important thing is to look at all the services that are offered around email and make certain they're available at the DR location. You may consider it critical, for example, to have patch or deployment technologies at the DR location.

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