I got a letter from the health insurance company. The Korean version contained "당연가입," which corresponded to "mandatorily [sic] subscribed" in the English version.
Although my native Korean friend had never heard the term "당연가입" before, he could guess what it meant. Whenever I discussed this topic with other native Koreans, they all used the term "의무 가입." (Even though I started the conversation with 당연가입 because I did not know 의무, yet.)
Is there any difference between 당연가입 and 의무 가입? Why wouldn't the letter just say "의무 가입," which seems to be more common?