An Auto-Responder is an automated message sent in reply to emails sent to a specific mailbox. Often this is used when someone is out of town or wants to send an automated response to all messages that come to a mailbox. In some cases it can also be used as an acknowledgement or receipt in the case of someone submitting orders or a support request.
This can be done by logging in to your account on the webmail site at http://mail.yourdomain.com
(or click here
Once you are logged in select SETTINGS - MY AUTO-RESPONDER from the top menu
Select "Enable Auto Responder" then click the Tab "Auto-Responder Message"
Type in the message you wish to be sent as an auto response then click SAVE at the top to enable it. You can disable it in the same fashion by unchecking the "Enable Auto Responder" option when you wish to deactivate the message.