How do I address a letter in Korean?
For example, the heading

Dear [nuguya],
blah blah letter body blah
Sincerely,
Me

I'm addressing it to a friend, so it doesn't have to be very formal. but all forms of this structure would be helpful to learn!
고마워!

Question

How do I address a letter in Korean?
For example, the heading

Dear [nuguya],
blah blah letter body blah
Sincerely,
Me

I'm addressing it to a friend, so it doesn't have to be very formal. but all forms of this structure would be helpful to learn! 
고마워!

Answer

I don't think 친애하는 is used in modern Korean, especially in a letter being sent to a friend. 

1. (내 친구) ㅇㅇ에게 

어쩌고 저쩌고... 

이만 줄일게. 

ㅇㅇ이/가. 
...............씀. 

2. ㅇㅇ(formal title, like 선생님, 교수님)께. 

어쩌고 저쩌고... 

이만 줄이겠습니다. 

ㅇㅇ 올림/드림.

Answer

친애하는 (person's name) 에게 => Dear person's name. or To ~

 actually, if its for you firend, there is no such form as "dear, sincerely .."
 just write as you speak to ur friend.    we never use 친애하는 to friend as long as it is in informal realtionship