Outlook for Mac 2016 uses different methods to store items based on the type of account that you have. With a Microsoft Exchange account, all item types are stored on the Exchange server, and Outlook synchronizes with the server at regular intervals. This allows you to access the items from another computer. And, if your hard disk is damaged, the information is not lost because the server has copies of all your items.
For IMAP and POP accounts, items other than messages are stored on your computer, not on the mail server. If you use multiple account types in Outlook, you might see folders labeled "On My Computer" in the navigation pane. This label indicates that the items in the folder are saved only on your computer; they aren't synchronized with a server.
To find out what type of account you have
On the Tools menu, click Accounts.
In the left pane of the Accounts dialog box, click the account. The account type appears under the account description. In the following illustration, the account is a POP account.
If you have an IMAP account, messages from that account sync with the IMAP server. In the mail view folder list, you will see a separate Inbox for each IMAP account.
If you have one POP account, messages are downloaded to the On My Computer Inbox. If you have multiple POP accounts, all messages from those accounts are downloaded into the same On My Computer Inbox. Since POP accounts do not allow Outlook to sync with the mail server, messages from all POP accounts go into the On My Computer Inbox. A copy of each message is downloaded into Outlook.
Note: To keep mail separate for different POP accounts, you can create rules in Outlook that automatically route your messages to folders based on the recipient address. For more information about rules, see Create or edit a rule in Outlook for Mac 2011.
If you have only Exchange accounts in Outlook, the On My Computer folders are hidden by default. This helps simplify the folder structure in the navigation pane. It can also help keep you from accidentally saving an item in a folder that is not synchronized with the Exchange server. However, you can choose to show the On My Computer folders in the navigation pane. You may want to do this, for example, if you want to create a contact group. Showing the On My Computer folders is required to create a contact group because the group does not sync with the Exchange server.
Tip: To show the On My Computer folders in the navigation pane, on the Outlook menu, click Preferences. Under Personal Settings, click General. Then, under Folder list, clear the Hide On My Computer folders check box.