That depends what email platform you are on. For BigPond Email;
- Log in via https://messaging.bigpond.com/
- Click My Settings tab at the top
- Select Auto-reply vacation message
Otherwise for BigPond Email with Outlook.com you;
- Log in via https://messaging.bigpond.com/ OR https://outlook.com
- Click the settings cog icon on the top right
- Choose Options from the drop down
- Click Sending automated vacation replies