My outlook 2016 desktop app was not syncing properly and having issues, so I uninstalled it; thinking it must be syncing properly with my 2 email accounts (1 outlook.com and 1 gmail).

Then I reinstalled new Outlook desktop (LTSC prof + 2021) and tried syncing - to my outlook.com account first and to my surprise it downloaded 35,000 emails from last few years. I believe at least 20-22,000 of these emails, I had already deleted in my previous Outlook app and organized others in folders - but I don’t see it on outlook.com!

To cleanly fix this - I have located the old OST file sitting in another C: folder from 4 days back, which is hopefully the best working copy with those organized emails.

Now even if I find a tool to do OST to PST conversion - my problem is how do I sync that PST (from PST file) to outlook.com and ensure that it syncs properly to re-organize all my emails and delete bad ones?

Then I can possibly - start a new OST file and carry on with good syncing.

Any help from experts (with the right order of steps) so I don’t mess this up any further?