Its Pretty Easy to Add New Email addresses. The way the Linux webserver works is it can deliver to a local user (mailbox with username and password) or forward to another email address.

Simply in webmin Create a new user for an email account.

System > Users and Groups > Create New User (bottom of list on right hand side)

Create User Webmin

Create a New User In Webmin


 

Then go to create the mapping see the list example

Servers > Postfix Mail Server > Virtual Domains > Add New Mapping

 

Postfix Edit Mapping

Setup Postfix Email Mapping