The Post-Rapture Post bills themselves as the postal service of the Saved. You see, when the rapture comes and all the
whackjobs goody-goody faithful are swept into heaven, they will have many friends and family left behind. (Remember, being a good and moral person doesn't actually secure your spot in Heaven.) So, the Post-Rapture Post is a service that will, for a small fee, deliver messages from the Saved to those left behind.
So, if you're pretty sure about your place in heaven and want to send a message to your friends and family that just didn't believe hard enough, head on over to the site. Or, maybe you want to send a "told you so" postcard to that silly Jew next door or the stubborn atheist down the street. Yes, they really have "told you so" cards. Most of their messages are less spiteful, however.
The great thing about the service is that you can be sure it will still be up and running after the rapture because it's run by atheists.
PS: Hey, here's a thought. Maybe the Rapture already happened and everyone who believes in it who is still here just didn't believe enough. Maybe it happened in 1937 and Amelia Earhart was the only true believer. Hmm.