When connected to Exchange messages will arrive with a slight delay in the mailbox.
This is caused by Outlook which will check for new messages every 30 seconds by default.
Online mode When the Outlook profile is configured in Online Mode Outlook will create a direct connection to the Information Store of Exchange.
This has as advantage that messages will appear almost immidiatly when delivered to the mailbox.
When a user is working on another workstation a new OST file will be generated if not available.Users can recognize this because Outlook doesn’t respond correctly.This can happen if one of the following tasks is being performed: Cached Exchange Mode i.c.w.In an Exchange Server 2010 organization it is normal for there to be some delay before administrative changes appear in the address book for Outlook users.For example, a staff member changes surnames and the help desk updates their Active Directory account with the new name.