Visit your webmail page at www.yourdomain.com/webmail and login using your full email address and password.
Once you're logged in, you'll see several options at the bottom of the page. Click on Auto Responders to configure your auto-reply.
Once you're on the Auto Responders page, you'll see a list of any responses currently set up. Click the Add Auto Responder button to create a new one.
You have several options when configuring your auto-responder.
When you've finished setting up your message, click Create/Modify to activate your auto-responder.
Once you've clicked Create/Modify, you'll see a confirmation screen, and will then be returned to your main Webmail interface. Click on Auto Responders again to confirm that your message was added successfully.
If you didn't set up a Stop Date, you can delete the message manually from this screen by clicking Delete.