Right-click Search Folders and "New Search Folder". Slide down to and
select "Create a custom Search Folder". Select Choose. Enter "All Mail" in
the Name field. Click OK. Outlook will prompt with "You have not specified
any criteria for this Search Folder. All messages in the folders you have
selected wuill appear in this Search Folder. Do you want to continue?"
Click Yes, then OK. You'll now have a search folder named All Mail that
will show everything in all mail folders of the mailbox.