If you want to automate the process, you can use mail filters to automatically put incoming mail in particular folders. (You can also use filters to tag a piece of incoming mail, or delete it, or mark it read, etc.).
An administrator can choose to view a user's mailbox, and from there they can rearrange the messages as they like.
Otherwise, that's a job for shared mail folders. That's a feature scheduled for an upcoming release. You can
vote for it in bugzilla to express your interest...