During a recent migration of Exchange 2003 to Exchange 2010 we needed to find out how many users had a mailbox and were not disabled.
In the end I used Active Directory Users and Computers snap in to create a saved Query.
1. Open ADUC and right click on Saved Queries and chose new –> Query
2. Give it a name and click on Define Query button
3. Select Custom Search from the drop down menu and then click on the Advanced tab:
4. In the box put in the following:
5. Click on Ok and the query should fetch out all users with mailboxes in Exchange 2003 and that are not disabled.