We set them up as a Heroku plugin, and the login into cloudmailin is done through Heroku.
Username and API keys are the same as the SMTP values.
You need to setup a domain to take the account out of test mode.
After a day they sent an email saying the DNS entries that neede to be changed:
mta.ourbigbook.com CNAME feedback-smtp.cloudmta.net
e210040093cm.ourbigbook.com TXT long-thing-in-attachment
But TODO even after that it still failed with:when we input
Domain has already been taken
Mta domain has already been taken
ourbigbook.com
.