When searching shared resources such as resource accounts, shared mailboxes, calendars, or public folders, why can't I see items older than a month?

This applies to email migrated to Outlook in the cloud, otherwise known as Exchange Online.

Microsoft designed Outlook to only return search results from shared resources such as shared mailboxes, calendars, or resource account mailboxes using cached mode.  If Outlook's cached mode can be configured for various windows of time (e.g., 1 month, 3 months, 6 months, etc.).  Search results from these shared resources will be limited to whatever that time interval is set to.

To increase the amount of cached content from shared resources, follow these instructions:

1. In Outlook, click the File tab.
   
   
   
2. Click Account Settings
   
   
   
3. Click Account Settings again from the drop down menu.
   
   
4. Click Change
   
   
   
5. Check the box for Use Cached Exchange Mode to ensure cached mode is turned on.
   
6. Move the slider to the amount of time you want cached.
   NOTE: the larger the time window, the greater amount of disk space you will consume.  This setting will not only download items from the shared resources library but your own as well. Only slide it to the window of time you want to be able to search shared resources' mailboxes.
   
   
7. Click More Settings
   
   
8. Click the Advanced tab.
   
   
9. Check the box for Download shared folders and then click OK.
   
   
10. Click OK
    
    
    
11. Click Next
    
    
12. Click Done
    
    
    
13. click Close.
    
    
    
14. Close and reopen Outlook.
    NOTE: The message in the status bar at the bottom of the Outlook window will show the caching activity.  Only once it reads "All folders are up to date" or when you click on a folder or account and it reads "This folder is up to date" has the sync completed.  Depending on the amount of data contained in your mailbox and the shared resource's mailbox and depending on your network connection's speed, this can take a long time.