Using classic Outlook for Windows in business environments
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IMAP was what you had said for incoming.
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Your account is added as an IMAP account - that is why you have the sync issues. POP is download inbox only, IMAP syncs all folders in the mailbox online.
Do you recall if you've always used IMAP or did you previously have POP and it got switched to IMAP?
Do you have any sync issues? Look in the Sync issues folder in the Folder navigation pane (Ctrl+6 to open it if the buttons are on the bottom). If your Outlook navigation buttons are in a vertical bar on the left, click the bottom icon in the vertical bar and choose Folder.
Errors will be in red text in the Sync Issues folder.
To switch back to the Mail pane, click the Mail button or use the keyboard shortcut Ctrl+1.