This article explains how to set up automatic replies in Gmail. The feature works by setting up a filter so that when certain conditions are met (such as when a specific person sends you an email), a message of your choosing is automatically sent back to that address.
How To: Create an Automatic Reply in Gmail
To have Gmail automatically respond to emails using a template based on a set of criteria, you first need to enable templates in Gmail. Here's how:
Select the gear icon in the top-right corner of the Gmail screen to open the Settings menu.
Select 'Show all settings' at the top of the drop-down menu.