Outlook Cache and Non-Cache Settings
Microsoft Outlook can cache (store) copies of your emails locally on your computer, so that it is faster to bring them up when you are looking through your mailbox.
There are advantages and disadvantages to caching. On the positive side, it is faster if Outlook does not have to go out to your mailbox in the cloud for every email. On the negative side, if you have a large number of old emails, or you cache a lot of Shared or Departmental accounts in addition to your own account, you are taking up a lot of room on your computer's memory to store all that mail.
A good middle ground is generally to cache your emails for the latest 12-24 months, and let Outlook search your cloud account for older emails. And if you access large Shared or Departmental accounts, you may want to disable caching. Your IT support staff can help you with recommendations if you are having speed or memory issues.
Changing from Non-Cached to Cached Mode
Go to Control Panel > Mail > Email Accounts.
Double click on your email account.
Check the Use Cached Exchange Mode checkbox.
(if done from within Outlook, click File > Account Settings > Account Settings; requires restarting Outlook)
Set to either 24 months or 12 months:
Click Next, then Finish.
Changing from Cached to Non-Cached Mode
If you have several and/or large Shared or Departmental accounts, you can disable caching for those accounts.
Follow the instrucitons above to get to your email account settings, then click More Settings… > Advanced.
Uncheck the Download shared folders checkbox.
Click OK, then Next, then Finish.