After moving mailboxes across Exchange organizations or administrative groups you have to manually update the Outlook 2003 profile when the user mailboxes are moved to a new Exchange 2007/2010 server.
If we have too many mailboxes to manage, we may use either of the following methods to automatically change Outlook 2003 users Outlook profiles.
1. Update the affected users' Outlook profile through the tool Exchange Profile Update tool (ExProfRe).
We can run the ExProfRe tool by using logon scripts or by using Group Policy. Or, you can run the ExProfRe tool at a command prompt to make the needed changes to an Outlook profile.
For detailed steps, refer to the following two articles
The Exchange Profile Update tool
ExProfRe Operation Guide
Note: The tool ExProfRe also works for Exchange 2007 users' Outlook profile
2. Another option is to update their profiles with a PRF file.
For Outlook 2003 affected clients, you can create a custom PRF file using the Custom Installation Wizard. This PRF file allows you to create a new profile or manage existing profiles. For more information on how to do this for Outlook 2003.
Customizing Outlook Profiles by Using PRF Files