The Tuesday Post: The Vatican Postmark

Did you know that you can send mail from the Vatican?  It does not go through Poste italiane. Poste Vaticane has it's own stamps and postmarks.  As far as I can tell, there is only one Vatican City Post Office.  It is on the south side of St. Peter's Square, just as you exit the Basilica.  When I was there in April 2013, there was also what appeared to be an "annex" in the shape of a motor home, a little east of the actual post office, also in the square.  I do not know if you can actually purchase stamps at the "annex".