Your email service can be managed using your web browser.
To access your Mail Control Panel for your mail accounts enter http://mail.domainname.co.nz/mailadmin/ (where "domainname.co.nz" is the domain name associated with your email service).
Before your domain has propagated or if you are experiencing DNS issues with your domain, you can use: http://mailx.hosts.net.nz/mailadmin/
From there you will be presented with the Mail Control Panel Login screen. Login using the Domain Admin details provided to you in your welcome email: