Using classic Outlook for Windows in business environments
What worked for me was setting the root folder path to "Inbox"
- Go to File > Account Settings > Account Name and Sync Settings
- Set the "Root Folder Path" to "Inbox"
As a side note, I have two email accounts on the same server. One works fine without the "Root Folder Path" being set, the other (the one I'm having issues with), requires the root folder path to be set. No idea why.