When you first sign up for your Hushmail Business account, you will receive a setup email at the alternate contact email address you provided. In that setup email, you'll find a link to create additional user accounts under Step 1 : Create Additional email addresses.
You can also create a new user account by logging into our webmail interface with the administrator account for your domain.
Once you sign in, please select Preferences from the menu in the upper-right, then click on the Domain tab. You'll then see a link to add an additional user account.