we are a SaaS site builder and for our customers we need to provide email service with their own domain names.
Most of the open source mail servers and tutorials are for having a server for one custom domain. we need to have the ability to add more domains and users on the fly.
Is this something Mail-in-a-Box can do? if so, how can we sync the logins and add users/domains with an API?
The users API isn’t documented but you can see how it works from this client:
If you get to actually doing this, you’ll want to also see the Custom DNS API examples which are documented inside the control panel (after you set up a box).