Outlook slow updating cached messages
It also insulates users from network latency and connectivity issues while they are using Outlook.By caching the user's mailbox and the OAB locally with Cached Exchange Mode, Outlook no longer depends on continuous network connectivity for access to user information.You can also deploy one mode or the other by using the Office Customization Tool (OCT) or Group Policy. But we can point you in the right direction if you want to learn how to turn on Cached Exchange Mode in Outlook 2013 or change how much email to keep offline.
Online Mode works by using information directly from the server, and, as the name implies, it requires a connection.
Mailbox data is only cached in memory and never written to disk.
If users work with a large mailbox, you can reduce the size of the local data file by using Cached Exchange Mode with the sync slider enabled.
The sync slider lets Outlook 2013 users limit the email messages that are synchronized locally in their Outlook data file (.ost).
If you decide to deploy Cached Exchange Mode, learn how to Configure Cached Exchange Mode.