The beta program of my new startup, Maildown, is now complete and is now accepting paying customers: https://www.maildown.app
As well as a lot of stability enhancements, we've added a new help system, a new CLI (https://github.com/chris104957/mailer-cli) and a REST API.
Maildown lets you create transactional and marketing email campaigns using Markdown syntax, so you can generate and send your email content far more quickly than with traditional WYSIWYG editors.
Thanks for looking, Chris