The following article explains the steps needed to add a user mailbox with a new E-mail Address alias.
1. Log into the Administrative Control Panel at https://my.securembox.com.
2. Under My Users, select User List / Editor.
3. From the User List you will see the Complete User List of every configured mailbox. Select the user you wish to add a new E-mail alias to and select "Edit User" link from the top.
4. Now select the Microsoft Exchange tab, then on the left select Manage Aliases.
5. Type in the desired address prefix and select the appropriate domain from the domain list. You can also choose which address is to be set as the Outbound or SMTP listed address. this is the address that all recipients see when they read E-mails from the set user. Select Save Changes when you are complete.