Users are added to secondary domains just as they are for primary domains. From the Users page of the Web-based Administration highlight the domain you would like to add a user to in the Domains list box at the top of the page and then click the Display button.
When the Users page for the secondary domain opens, click the Add New button. The Add New User page will open.
Select User from the Type box and then provide a valid username in the Name text box. Click the Add button to accept the new user. The User Edit page for newuser will open.
From this page you can configure the user account that you just added to the "seconddomain" secondary domain just as you would any other user account. If you would like to add more users to this secondary domain click the Add Another button and repeat the procedure.
From the Control Panel Applet, right-click in any white space in the window and select New > User from the popup menu. The new user account will appear in the window.
Enter the username for the new account and hit ENTER on the keyboard. The Edit User dialog box will open.
In the Edit User dialog box you can set the account password, mailbox for incoming messages, and specify a mailbox for carbon copies. You must click OK on the Edit User dialog box to add the new account.
Note: When the user configures their email client they will have to use Domain name\ Username for the account name to receive and send mail properly.