An auto responder (e.g. Out of Office) needs to be set up at the servers where you email lives, not in your email program.

1.) Log in to your domain’s control panel: http://www.yourdomain.com/webmail. Your login name is your email address ([email protected]) and then enter your password.
2.) Click on the “Autoresponder Options” button.
3.) Type in your email address in the From field and the message you want people to receive in the Body field and that’s about it.

4.) When you’re back in the office, come back to this page and delete the responder. I haven’t found a way to save these easily so you could come back and choose the auto response “Out of Office” again. For now, I’d save the info somewhere handy where you can cut and paste the text you need.