Using classic Outlook for Windows in business environments
This same thing just happened to me. I've been using Outlook on one Windows PC with several email accounts for months: 2 Gmail, 1 Yahoo, 1 iCloud. I purchased an Office 365 subscription a few days ago to use Outlook on a few other computers (Mac OS & Windows). Now all emails from the two Gmail accounts are gone. The Yahoo & iCloud accounts seem to be unaffected.