You can manage email addresses from your cPanel account.

• Access your cPanel by visiting http://[yourdomain]/cpanel
• once logged in, select 'Email accounts' within the MAIL section
• fill in the form, selecting the appropriate domain (if applicable)
  email name, password, confirm password, mailbox quota
• click 'Create account'

Using webmail
You can login to webmail by visiting http://[yourdomain]/webmail
login: youremail@yourdomain.co.nz
password: your email password

If you can login here your email and password are working


Setting up Email Client
See this article: How to setup email: pop/imap & smtp