Wow, perusing through Southern Phone's site is remarkably annoying. Trying to fine relevant information on something as basic as manual email settings is a journey into a rabbit hole.
http://www.southernphone.com.au/
Hope their tech support can help you but if not, I'm going to suggest you give some serious thought to just switching to Gmail or Outlook, or some non-carrier service. When you use the email service tied to your phone carrier or your ISP, if you change services in the future transferring your email account, and possibly contacts and calendar, could be complicated or problematic. With a service such as Gmail however, you can access it no matter which phone carrier you're signed up with.