In listening to a television report in Las Vegas where postal managers were interviewed, they all stresses that  mailing sooner than later is the key for ALL types of mail at this time of the year due to the the sheer volume of items being sent.  Based upon the lines I personally experienced when buying stamps yesterday, I would have to agree.  A clearly addressed letter or package is key to a timely delivery.  If it can not be read or if the wrong zipcode is used, this could add days, weeks or simply make the delivery impossible.  If you don’t know zipcode, you can easily obtain it by going to the “Find a zipcode” tab on the www.usps.com website.  Another piece of advice from the interview was that is you do not know the zipcode and cannot look it up, simply leave it off and the postoffice will put it on your item for you.  They would rather do this than have you provide the wrong one. Perhaps a bit strange, but seems to make sense at the same time.