Here we have a much more complicated recipe that implements a form of vacation service to inform senders that you are away and unable to reply to e-mails. At first thought this could be a simple non-delivering recipe to send a message back to all messages received. However, this is not ideal as some people may end up receiving multiple delivery confirmation messages and you may also end up sending messages back to system utilities that have no way of understanding your well-meant reply.
The example is based on the "vacation example" from the Procmail
procmailex manual page.
vacation.cache file is maintained by Formail. It maintains a vacation database by extracting the name of the sender and inserting it in the