'Cached' mode will allow your Outlook client to download a local copy of your e-mail messages from a specified time frame. This will improve the performance of Outlook in remote work scenarios by reducing the required amount of interaction with mail servers over your internet connection.
- In Outlook, go to the 'File' menu in the upper-right, and select 'Account Settings'.
- Select your primary mailbox (firstname.lastname@example.org) and then click 'Change'.
- Under 'Offline Settings', check the box next to "Use Cached Exchange Mode..." and set the slider to "1 year".
- Click 'Next' and restart Outlook when prompted.
NOTE: if you have any proxy mailboxes added, follow the same process for those accounts by choosing the mailbox in step #2. It's recommended to set the date range to '3 months' for proxy accounts.