...All you need is a PHP environement and a little postgresql database.
The concept is fairly simple:
* You configure your mail server to send a copy of every mail that it processes to a specific mailbox
* You set up autoreplybot to poll this mailbox, either via POP3 or IMAP
* Users log on the autoreplybot web panel using their mailbox credentials (which autoreplybot validates against the mail server) and write their 'out of office' messages in a simple html form.
* When one of your users configure an "out of office" reply, autoreplybot sends this message back to every person that write an email to the user.