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Make sure Outlook is closed.
Search Windows for Control Panel, and click to open
Click Mail (Microsoft Outlook 2016)
Click Data Files
Select your email account from the list and click Open File Location...
In the Explorer window that pops up showing the email file's location, at the top, select the View tab.
Make sure File name extensions is checked:
Your OST file looks something like this:
Rename your OST file to .old (i.e: example@otc.edu.old)
Relaunch Outlook. A new OST file will be generated. It may take some time for all of your email to re-sync.
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