Since I use the bureau for outgoing QSL, you need to know that many countries have laws pertaining to who can receive QSL cards. If you are not a member of your national radio society, you might not receive cards I send.
According to the information on the ARRL web site, the following countries require stations to be members of their National Radio Society to receive cards via the Bureau.
Denmark France Germany Hungary Italy Japan Monaco
Norway Poland Portugal Russia South Africa Sweden Zambia


