Mail usually arrives either by airplane or by ship, depending on the research station's location.
Your return address in Antarctica is based on the logistical operation of mail in your research station. Your station manager can give you the proper return address for your mail.
Telephone, Email, Snail Mail.
There is no ownership of an 'Antarctica post office'. Each research station organizes the logistics of sending and receiving mail.
Your answer depends on the 'stuff' and where in Antarctica you propose to send it. Every research station has mail service delivered by the government funding the station. That nation's postal service may define the 'stuff' limits that you can send to your correspondent on the continent.
Your answer depends on the service provider who supplies postal service to the location from which you want to send mail. Each research station employs a mail service provider who will dictate postal rates, that vary depending on the destination of the mail.
The only way to get off the Scientology mailing list is to move somewhere there is no mail delivery like Antarctica. You will still technically be on the list but if you can't get mail it won't bother you. There is no other way.
Your answer depends on the address of the recipient. Your local postal authority can answer your question, given its weight and destination.
Depending on which station you want to send mail to, you can obtain the military postal service address from the recipient. Generally, service is provided by the Air/Army Post Office™ or the Fleet Post Office.
There are no newspapers that are specifically printed in Antarctica. However, researchers and staff stationed in Antarctica may receive newspapers from their home countries via electronic means or physical deliveries.
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. Other countries have their own mail and postal designations for their stations on the continent.
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When addressing post materials for a worker in Antarctica, the mailing address will be available from the government for which the worker is employed there. For example, workers employed by the National Science Foundation -- the United States representative on the Antarctic continent, receive mail addressed through the US military postal system.