Patrick Price writes:

The same way as implementing an autoresponder with any other mail server. You can invoke it from a .courier file. If you feel brave, you can set up an alias that directly feeds the autoresponder (which will then run as the mail userid).

You can certainly take advantage of the preinitialized environment variables in order to automate the response, and take advantage of some bundled utilities. reformail will generate the autoresponse header, then just append your text to it, and run sendmail to mail out the result.