The following was provided by the USPS:
The United States Postal Service is offering postmarks from the North Pole through Dec. 10.
To receive the holiday postmark from the North Pole, customers should affix the correct postage to addressed envelopes and cards; then pack them in a larger envelope, box, Priority Mail or Express Mail package and send them to:
North Pole Holiday Cancellation
4141 Postmark Dr.
Anchorage, AK 99530-9998
To ensure delivery by Christmas, all requests must be received in Anchorage by Dec. 10. The service is provided at no cost.