Auto Responder when computer is sleeping

Hi,
I know how to set an auot away message using rules but it requires that my computer stay turned on and not sleeping for it to work. The computer has to be able to retrieve and get the email before it can send a message back.

Anyone know of a way around this? Our mail work ***** and the company we are using doesnt have auto respond built into the webmail.

I checked out the little app called mac Responder and again, the computer has to be turned on.

I was thinking maybe there is a way to use automator for this? Maybe it checks for mail every hour or so then if it sees any it performs the sending of the away message? Itrhink this would work but I don't know enough about automator to figure it out although if I had to I guess I could. lol.

Maybe there's some sort of app we can use that checks on the mail server or something?

Thanks for any info,
David