Auto-responders are basically webmail's answer to "Vacation Mail" in Outlook. The web mail has the advantage of being on 24 hours a day. It is a great alternative to an Exchange Server.

Create an Auto Responder:

1. Select the Auto Responders Icon found on the login screen for webmail.
(Likely at http://yourdomain.com/login

2. Press Add Autoresponder

3. Fill in the fields

Subject should be %subject%. You may add anything you want to this line, such as "Out of Office" - %subject%. This will place "Out of Office" before the original subject.
From should be %from%
Body should contain your out of office message.

4. Press Create/Modify to add.