Migrated users Outlook is still pointing to the source Exchange server. (4351483)

User has been migrated but when migrated user opens Outlook it is still pointing to the source Exchange server.
Why does this happen?

The process of migrating a mailbox consists of many steps.

First directory synchronization matches the objects and mail-enables the target users.
Then the mailbox is added to a mailbox collection and the content of the mailbox is synchronized by Mail and Calendar agents.
When this is done the mailbox can be switched, either automatically or manually. When switching a mailbox migration tool places a hidden message inside the switched mailbox.
After mailbox switch Client Profile Updating Utility must be configured and executed in order to update Outlook profiles.
CPUU will find the switch (hidden) message in source mailbox, this message contains the information about the source and about the target servers.
CPUU, when executed successfully, updates the users Outlook profiles and re-directs the profile to point to the target mailbox.

Please refer to Client Profile Updating Utility - Administrator Guide at https://support.quest.com/technical-documents/client-profile-updating-utility/5.7.8/administrator-guide