Quoting The Angry Professor:
I need a gmail filter that sends a custom vacation message to certain people. The filter needs to scan the message for the latest date mentioned and determine the geographical location of the sender. It must next add four weeks to that latest date. The longitude of the sender’s geographic location must be advanced by 180o and the latitude multiplied by -1. After triangulating the dry land nearest to the rotated coordinates, the filter must finally send the following “vacation” message:
Thank you for your email. I am [on dry land nearest the point exactly half-way around the globe from you]. I will not have email contact until [computed date], but I will try to respond to your message as soon as I return.