When you configure MS Outlook with an Exchange, IMAP, Office 365, or Exchange Outlook account, the account is set up in Cached Exchange Mode by default. Also, an Offline Storage Table or OST file is created that stores a synchronized cache of mailbox items, such as emails, attachments, contacts, calendars, tasks, etc., on your local drive.
Besides user mailbox data, Outlook 2010 and later versions also download and store any shared mailbox or shared mail folder by default in the same cache (.OST file). Users can see the shared mailbox folders in their email account and access the mail items.
When in Cached Exchange Mode, changes made in Shared Mailbox by other users are not synchronized immediately and thus, may not be visible to other users accessing the Shared Mailbox. That’s why some users may see folders while others can’t see them due to delays in synchronization.
