Click on the Configuration icon from the Navigation bar and then click Edit Settings.
WebMail home page
Select Email from the Settings menu on the left side of the window (A).
Click Autoresponder from the Email settings drop-down menu (B).
Check the box on the screen next to the Settings menu to enable the autoresponder (C).
Your e-mail address will come pre-filled in the sender textbox but you have the option of using your name, business name, etc. Enter a subject line and then you can create your autosresponder message in the large texbox provided towards the bottome of the screen.
Once you've created your autoresponder you can simply exit the program. The autoresponder will save automatically.
For additional information, you may want to reference: