Outlook 2013 includes a new feature, Sync Slider, that limits the amount of mail synced with Outlook, in an effort to limit the size of the offline cache file used by Exchange or IMAP mailboxes.
To check the sync settings, open File, Account Settings dialog and double click on the email account. Slide the control to determine how much older email is stored offline.
Exchange server shared folders
When delegate folders, shared mailboxes, and public folders are used, Outlook caches the contents of these folders in the ost file, however, the sync setting does not apply to these folders, and all contents of these folders are stored in the local cache file.
Users who need to limit the amount of data cached locally can set up filters on each folder. To do this, right click on the folder and choose Properties, Synchronization tab. Click the filter button and create a filter.
Because only Public Folder Favorites sync, remove folders not needed offline from the Public Folder Favorites list will help to reduce the size of the cache. You can also disable caching Public Folder Favorites or Shared folders in Account Settings > More Settings.
Note that in addition to Delegate, Shared, and Public Folder Favorites, the non-mail folders and the Outbox are exempt from Sync Slider setting.