I just installed the MIAB on DigitalOcean and it worked. This place has a great support too.
Now, I am interested in hosting email mailboxes for people from another domain name.
Ultimately, I want to be able to host series of mailboxes on domain names different from the one MIAB is installed on.
How do I do that ?
You will need to add a MX record directing mail to your box in the DNS records of each domain added. There will also be other records that need to be added/changed. What exactly depends upon other factors, such as are the domains also hosting websites, or are they used exclusively for email. There really is no one size fits all answer to your question. It is determined by other factors. And yes, reading the External DNS documentation will help assuming that you understand that there is no one answer …