Group Roles in Exchange Server 2007

Exchange Organization Administrators 

This group is having the highest level of permissions and full control on exchange organization. Users of this group can also grant permissions to other Exchange administrators. This group gives members the rights to create, modify, delete connectors, server policies and global configuration options. Assign this role to limited number of users as it may impose security threat. 

Exchange Recipient Administrators Role

Members can modify exchange-related properties on any Active Directory components like users, distribution groups, and public folders. Members can permission the ability to change Client Access mailbox settings and Unified Messaging mailboxes.

Exchange View-only Administrators Role

Members have reads-only access to the Exchange organization and on Exchange recipients.

Exchange Server Administrators Role

Members can administer one or more exchange servers but cannot modify global configurations. Members cannot uninstall an Exchange Server, they can add or remove server roles.