When I first read the title of this thread, I was thinking this was just another nutty conspiracy theory, but when I read the story, it doesn't sound nutty at all. We know Oswald was angered by the FBI keeping a watch on him. Maybe he was trying to determine if they were checking his mail. By addressing this package to a phony address, he would have known if it arrived at his current residence, somebody was keeping track of him and knew where he lived. Who knows what was going on inside his head shortly before the JFKA, but this certainly seems like a plausible explanation.
I can't make out the date on the metered stamp but if it was postmarked for the week of November 22, it would really have some significance.