Sorry, I don't know much about this stuff....what is an IRC?

I am sorry, I am sending from the United States and I did not mean return address. I meant the return envelope. How much postage should I put on the envelope that will be sent back to me.

I was going to send something to Pope Benedict XVI. Could someone please give me some guidance on what kind of postage I need to put on the envelope? What about the return address? Any help would be appreciated!

Thank you!