How to retrieve shared mailboxes in exchange 2003?

Hi,

How do I retrieve shared mailboxes in 2003 without knowing the actual mailbox or the users?

Scenario is something like there's around 8000 mailboxes and we currently don't have a trace of the mailboxes that are common.

We are migrating mailboxes and we are going to migrate the shared mailboxes together with users that has access to it.

Thanks.