All countries that support scientific research on the continent have their own mail and postal designations for their stations. ZIP Codes are a phenomenon of the US Postal Service.
For example, McMurdo Station in Antarctica, which is run by the National Science Foundation and supported by the US Military, has a military designated zip code, which changes annually. All NSF stations research stations there supported by the government of the United States have their own, annually-designated postal assignments.
Technically, you are posting to a military base: APO-Army Post Office; AP-Armed Forces Pacific. Service is for any temporary scientist or worker in support of science, whether military or civilian.
The mail transits through New Zealand where it is transferred to Antarctica via US Military C-17 transport/cargo planes.
Related Q&A：
What is the ZIP code for antarctica？-Oh, well, Antarctica doesn't have a standard ZIP code like you'd find in other populated areas. You see, Antarctica is a very unique and extreme environment with very few permanent settlements. It's mostly visited by researchers and scientists for specific purposes. So, when it comes to ZIP codes, they just don't apply there. It's not like you can send regular mail to Antarctica using a ZIP code. The postal systems and addresses in such a remote and inhospitable place are quite different from what we're used to in our everyday lives.
