The Power of the Postscript
“The primary thing not to do with your P.S. is state a new fact, introduce a new idea or start fresh with a different thought,” Jutkins cautions. “The P.S. is a place to repeat the call to action, remind the reader of the key benefits and ask for a [gift].”
The reason for this, he says, is because for those four of five who read it first, you share news and then fail to talk about it elsewhere in the letter. You confuse the reader when you introduce new material and cover it only in the P.S.