How to Send Outlook Newsletters with Email Communication Services

Outlook Newsletters are intended for internal communications, at least for the preview. It's possible to take the HTML for a newsletter and send it with Azure Email Communication Services (ECS), the PAYG service for bulk email. It sounds like a good way to use Outlook Newsletters to share information with customers and other external recipients. Some manual intervention makes everything works. It would be great if Microsoft tweaked Outlook to remove the rough edges.