First, clone this project and edit the .forward file
$ cd ~
$ git clone https://github.com/adiehl/autoreply.git
$ chmod 755 autoreply/autoreply.php
$ vim .forward
Put this single line into the forward file:
|~/autoreply/autoreply.php
Copy the file settings.json.example to settings.json and configure at least your sender email address.
You should also customize your message.txt