With dynamic distribution groups, group membership is determined by the result of an LDAP query. You can create a dynamic distribution group and define the query parameters by completing the following steps:
1.) Open the Exchange Management Console
2.) Navigate to Recipient Configuration, Distribution Group
3.) Click New Dynamic Distribution Group
4.) Give up a Name and Alias
5.) Change the Filter settings. In this example I’m using the Active Directory attribute Department
6.) Give up the Filter Condition. To see a preview of all the effected users, click Preview
7.) Click New to finish the last step