Hawk Enterprises has built this wonderful little script that you can install and run vacation notices, or any type of auto response via php and CRON. The premise is simple, login to the users account, look at the emails, parse for the address then send out an email to the people in the pop3 box. Requires the use of a 3rdparty (free) pop3d wrapper. I would recommend this for anyone that has an account on a VPS or Shared Hosting situation were they only have access to PHP and CRON.