While removing Exchaneg 2003 you get : „One ore more users currently use a mailbox store on this server – the userser muste be moved…“

1. Run Active Directory Users and Computers.
2. Right-click your domain towards the top of the left-hand pane and choose Find from the context menu.
3. In the Find Users, Contacts, and Groups window, click the Advanced tab.
4. Click the Field button and then choose User. From the list of attributes displayed, choose Exchange Home Server.
5. Set the Condition field to Ends With and then type the name of the old Exchange server into the Value field.
6. Click Add to add this condition to the Condition List.
7. Click the Find Now button and you should be presented with a list of objects that still have Exchange attributes. You will need to clear these before you can remove the server. Note that you don’t need to worry about system mailboxes.

Goto the properties of the Mailbox Store – Limits and change „Keep deleted mailboxes“ to 0

Then right click on the Stores Mailbox folder  and choose „Run Cleanup Agent“