First, you need to set up your profile to tell us where we're sending push notifications.
Then, set up a filter to tell us what messages should send a push notification.
In the filter, for the action, select "Push Notification with label", then enter the label you want to appear on your push notification.
The push notification you will receive will say:
Pobox.com - <label> (if you don't provide a label, it will say "Filter matched") From: <From field of matching email> Subject: <Subject of matching email>
Push notifications are only sent once every 5 minutes, as most push systems will throttle programs that receive too many notifications too quickly.