We're looking for an email application, that also doubles as an archive. Where each person would have their own mail, but when permissions allow, they would be able to search the entire archive.
One concept would be something like a single mailbox, with aliases for all the incoming mail, or just a catch-all. Then each mail client / user, would just have a view of that mailbox of the mail they sent or received. Then an administrator could create new views and assign them to users to see other emails.