To create an automatic responder for your email, log in to your Webmail interface, click on the icon gear on the top right and choose Preferences:
Click on Vacation Responder and use the selector to turn on:
You can set the start and end dates, add a custom subject line, and compose a message to be automatically sent out. For contacts that send multiple messages, you can also control how frequently they receive the autoresponder.
Once you've added all the information, click on Save and that's it! All the messages sent to that email address will receive the scheduled automatic reply.