I have an Exchange 2007 installation with 20 mailboxes. Users connect
to exchange using outlook 2007.

There is an add-in for outlook that allowes every user to set two
defined custom fields (UserProperties) on every email in his own
mailbox (basically, it is just a form region with two dropdown
fields).
Is there any way to allow all users to perform searches across all
mailboxes in exchange using outlook. Besides, is there any way to
create a view in outlook that will combine all messages from all
mailboxes and group them using this thwo custom fields?

Thanks in advance!