I don't think Jason Yu's steps are necessary any more.
For those of you who haven't discovered it yet, the Cumulative Updates to Windows 10 Build 1809 (KB4471332) and Cumulative Update to .Net Framework 3.5 and 4.7.2 for Windows 10 Build 1809 (KB4470502) that Microsoft pushed down on December 11-12 seemed to
have solved the outgoing iCloud email (SMTP) problem. If you haven't yet do so, download and install them.
For those of you who have been mucking around in Outlook settings and still can't get it to work: after downloading the cumulative updates from Microsoft, delete the iCloud mail account in Outlook, sign out of iCloud for Windows, reboot, and then sign back
into iCloud for Windows using your regular Apple Id. and password, and let it install everything for you. You will get iCloud mail, contacts and calendar in Outlook, and can elect photo streaming from your Apple device through iCloud to your Windows compute.
I do not have two factor authentication so no app specific password for me, but you don't need it, iCloud for Windows did all the work, no fussing around in settings.
If you haven't been using iCloud for Windows to do the installation in Outlook, get it here: https://support.apple.com/en-us/HT204283. Do not fiddle around with the mail settings in Outlook. Just let iCloud for Windows do everything for you. Report back
to this forum if it works. If you want to look at the mail settings and test them, use Windows Control Panel, search Mail, click on it then click on the Mail Accounts button, double click your iCloud account, then click on the Test Account Settings button.
This only began to work for outgoing mail (SMTP) after installing the latest cumulative updates. Incoming mail, contacts and calendar worked before then. I think Build 1809 broke something and Microsoft has now fixed it. Report back us on this forum.
Good luck.