Symptom:

The Fix:

Run: control.exe > click on Mail


Click on Show Profiles

Click on Add

Input a profile name and click OK

Toggle the radio button next to Manual Setup > Next

Select POP or IMAP > Next

Fill out this screen as shown > click More Settings

At the Internet Email Settings window, click on Outgoing Server and copy this configuration > click on Advanced when ready

Fill out the port numbers and other settings > OK

Click Next  > OK > Set this New-Profile as Default > OK

Run Outlook as Normal and allow it some time to download the entire mailbox from the Office 365 Exchange server.