Especially when it's such an easy issue to fix, it's called using vacation mode, however the message that you post is not that your away, but rather your very busy and due to the volume of email, that you will respond in person at your earliest opportunity. People can be amazingly tolerant when they know what is going on, they can be amazingly intolerant when they don't. You can include even, that new orders taken today, will be for shipping on a certain date, even if that date is in December, and that if the customer is in a hurry to call and give the phone number to call.