The Outlook 2016 email settings are maintained in a registry key.
You can export that key and import it back in to Office 2016 on a reinstall. This will put all of the settings for your previously configured email accounts, and data files, back into Outlook.
The key is: HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Profiles\Outlook
This key does not store any the actual emails, just the email account and data file (pst and ost) settings in Outlook, which will save you from having to reconfigure all of that stuff. If you are using pop3 accounts, the emails will be in your pst files, which you must backup externally before you reinstall Windows. The pst and ost files will not be deleted, but will remain if all you are doing is uninstalling/reinstalling Office 2016. If you are using Exchange email, then your emails will be in an ost file, retained locally and online.
Keep in mind that when you reinstall Office, even though you have local copies in your backed-up pst file, it will probably download ALL of the emails in your online pop3 accounts (which could be several thousand). If you have your pop3 Outlook settings configured to delete the emails from the server (after 14 days is the default) after you retrieve them, then your old emails will be in your backed up pst file, and the new Outlook install will only be downloading the 14 days of emails that you left on the server. If you don't backup the pst files, and you have your pop3 accounts configured to delete your emails after 14 days, then you will have lost all of your old emails forever.
And that, my friend, is why you should always back stuff up.
Original post found on Microsoft Answers:
https://answers.microsoft.com/en-us/office/forum/office_2016-outlook/how-to-backup-email-account-settings-in-outlook/d3a63184-da06-4ba8-93ba-7c3494185af5?auth=1
