Role of Expansion Server

This article explains the function and role of expansion server in the exchange server 2003.

1. Expansion server generally routes the message that are sent to a single distribution list or group of users listed in that group.
2. It is also responsible for expanding the group to its individual members and also will resolves the name of the recipients.
3. Importantly it is used to determine the most efficient path for routing the messages.
4. To find the expansion server for a distribution group, Right click the distribution group àproperties à Exchange advanced à Expansion server à click the drop down button to list.
5. In detail,
a. When user selects group from GAL in outlook. The outlook obtains the GAL via NSPI(Name Service Provider Interface) request sent to a GC.
b. Once the name verification succeeds, it will turn the recipient address bold.
c. When user sends, outlook uses MAPI to transmit the message to the user’s home exchange server.
d. Exchange server sees that the recipient is a group, and it sends an LDAP query to GC for the member’s list along with the email attributes.
6. By default any server can in the exchange organization can acts as a expansion server. This option is recommended because it totally avoids the single point of failure. Assigning particular server as a expansion server for particular group will result in failure if that particular server is unavailable.