Here is information about how to add new user who has a different domain name in their email address. For example, if you use @abc.com and the new user has an email ending in @def.com:
1 – Click on the Users tab
2 – Click on Add New User
3 – Enter the person’s full name
4 – Scroll down a bit then click on Add New Domain
5 – Type in the new domain name (using the example above you would type def.com)
6 – Click on the Add button
7 – Type in the first part of the email address
8 – Use the dropdown menu to choose the new domain that you just added
9 – Click Next then finish choosing other services for the user and choosing the type of account (User, Group Admin or Administrator) then hit Add
