ANSWER: Yes, it is a crime. Below are the relevant (Korean) laws.
Act on Promotion of Information and Communications Network Utilization and Information Protection, etc.
(정보통신망 이용촉진 및 정보보호 등에 관한 법률)
Article 48(1): No one shall intrude on an information and communications network without rightful authority for access, or beyond permitted authority for access.
—> Max criminal punishment: 3 years or 30 mil won
Article 49: No one shall damage another person’s information that is processed, stored, or transmitted through an information and communications network; nor shall anyone infringe, misappropriate, or divulge another person’s secret.
—> Max criminal punishment: 5 years or 50 mil won
– Translation mostly by KLRI (Korea Legislation Research Institute)
Article 48(1) deals with just “accessing/reading,” while Article 49 deals more with “tampering/divulging.” Hence the harsher punishment.
But either way, the actual punishment most times is a (criminal) fine. Late last year, a man (here in South Korea) was fined 2 mil won after he secretly read, copied, and divulged (to friends) his wife’s emails and Facebook messages. (His wife was having an affair, it seems.)
But here is the important part: Even such evidence illegally acquired can be admitted in civil suit. This is especially important here in South Korea because a unilateral request for divorce is not easily granted. You need to prove your spouse is/was mainly at fault for having ruined the marriage (e.g., marital infidelity). Proving infidelity is also important because you can simultaneously sue for “psychological pain and suffering.” Against both your spouse and his/her lover. Adultery is no longer a crime in South Korea, but it still remains a tortious act. That’s why it’s incorrect to say, “Adultery is legal in South Korea.”
FYI: In the case I mentioned earlier, the man was fined (as much as) 2 mil won because he went so far as to divulge that information. Had he just kept it to himself (to use as evidence in court), the criminal fine would have been much lower. He could even have received a deferred sentence. Meaning, the crime can be expunged after a period of time.
“May divorce be with you.” (Only if you feel it’s necessary.)
Do you remember your first email account? The first email account I ever had was one given to me when I was a high school student in Beijing. After that, I used HoTMaiL mostly. I now use Gmail and Naver Mail. In Naver Mail, one neat feature is the “mandatory delay” option when sending. I set mine up so that every time I click “send,” the email is actually sent 5 minutes later, and I can rescind anytime before that.