Lesson about Writing Letters or Emails?

[lewinbrau]

I often write letters or emails to my future father in law who lives in Seoul. Unfortunately, I don't know the proper way to close the letters I write to him. Even in English, it is difficult to chose the correct closing depending upon the subject of the letter and who it is intended for.
I am wondering if there is already a lesson about this and if someone wouldn't mind helping me out with a few appropriate words to close a letter written in Korean to my aboenim.

Thank you!