Configuring mail server settings
You would need to set at least one mail server. Under Mail Servers tab, click Add New Server button. You'll need to supply IMAP and SMTP server connection details, as well as the complete list of domains that belong to this server.
Note that you will not need to add users manually - instead, users simply log in from main page by specifying their email and password. And based on domain part of their email address, a certain mail server is used, out of those you have added in this step.
To allow users sign-up to your mail server, you can follow this step.
afterlogic.com