This might be happening due to corrupted settings or files associated
with the Outlook navigation pane
You can correct the probelm by using the Outlook switch : /resetnavpane
to restore the settings to default.
Follow the given steps to do so:
1. First, Exit Outlook.
2. Click on the Windows Start Menu
3. Click on Run and type outlook /resetnavpane in the box.
4. Press enter.
This will reset the Outlook navigation pane settings. I hope this will
resolve your issue.
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amanda_lakai