Exchange Server and Active Directory
Exchange Server requires Active Directory. Exchange Roles (HT, CA, MB) use AD DS except the Edge Transport Role that uses AD LDS. An Exchange Server Organization and an Active Directory Forest is a one-to-one relationship. Despite that last fact, many exchange organizations can be managed from the same exchange management console. Exchange installation modifies the schema and creates exchange server specific objects and adds exchange server specific attributes to already existing objects. The configuration partition includes Exchange Server configuration objects: global settings, e-mail address policies, transport rules, and address lists. The domain partition includes recipient objects, mailbox-enabled users, mail-enabled users, groups, and contacts. The email attributes of the mail-enabled and mailbox-enabled recipients replicate to the Global Catalog. The GAL is generated from the GC. HT Servers access the GC in order to locate a recipients mailbox for delivery. CA servers access the GC to locate the user’s MB server and to display the GAL to clients. For this reason we need at least one GC server to each AD site. The new RODC of Windows Server 2008 cannot be used with Exchange server.
Exchange Server and the Domain Name System
Exchange uses DNS to locate AD and GC servers. Exchange is site-aware so it tries to contact the servers on the same site. When Netlogon Service is started on the DC, it updates the DNS with SRV records that describe it as DC and GC. For Exchange to function, an internal DNS that supports dynamic updates is needed. SRV records in DNS identify servers that provide specific services.
SRV Records use the following format:
_Service._Protocol.Name TTL Class SRV Priority Weight Port Target
Explanation:
_Service=Service Name like LDAP, Kerberos, etc.
_Protocol=TCP or UDP
TTL=Time to Live in sec
Class=IN (Internet)
Priority=Clients attempt to access servers with the lowest priority number
Weight=complementary mechanism to priority that provides Load Balancing. Clients access randomly servers that have the same priority and higher weights
Port=Listening TCP or UDP port
Target=FQDN of the system that provides the service
After that, exchange queries the DNS for the A or AAAA (Quad-A) record of the server to obtain it’s IP Address.
When Exchange Server authenticates with the domain it stores the site name in the registry, so when it queries AD it will ask for local AD site first.
Exchange also makes use of MX (Mail Exchanger) Records in order to deliver Internet messages when using the SMTP Protocol. The MX record contains the host name that accepts inbound e-mail for a specific domain and a preference value. When deploying multiple SMTP servers the one with the lowest preference value routes all messages unless it is not available. If equal preference values are used, load balancing is applied.
To support spam mail filtering, SPF (Sender Policy Records) for acceptable domain names and Reverse Lookup Records for SMTP Servers can be configured.
