I may be behind the times but I just found out this year that you can receive letters from Santa postmarked with a north pole address. You have to write a letter to your child and put it in an envelope with the proper postage and then mail that letter in a separate envelope to this address:
NORTH POLE HOLIDAY CANCELLATION
4141 POSTMARK DR
ANCHORAGE AK 99530-9999
Here are the instructions from USPS – very cool!