The X1 Professional Client allows you index and search Exchange Public Folders, but will not do so by default.
Enable Exchange Public Folder indexing by following the steps below within X1:
1. Click on Tools > Options > Email > Outlook
2. De-select the checkbox "Ignore Public Folders and additional mailboxes"
3. Click "Apply"
4. Click on "Select Folders To Scan"
5. Select any public folders or additional mailboxes that you would like included in your index and click OK
6. Click on "Index Outlook Now" to update your email index
Please Note: When indexing completes, your Exchange Public Folders and additional mailboxes will be included in your search results.