DRA and ExA allows you to manage many network objects, including contacts and the associated email addresses. Contacts are available only in mixed mode or native Microsoft Windows domains. Contacts do not have a Security Identifier (SID), as do user accounts and groups. Use contacts to add members to distribution lists or groups without granting them access to the network services.
You can add contacts to security or distribution groups in mixed and native mode domains. Because security groups can be used as distribution lists in Microsoft Windows, you may want to add contacts to these groups. Having a contact in a global security group does not prevent the group from being converted to a universal security group when you migrate to a native mode Microsoft Windows domain.