Okay here is my dilemma, I am going to a write to a Japanese friend a birthday letter but I don't know how should I construct it; I've tried to search around the net and I found both formal and informal letters.
Now the problem is that friend of mine happens to be my boss in my Job too which means in my case I don't know which kind of format should I use in writing the letter.
Do I use the formal style with 拝啓 opening remarks or just write my message to him instantly (without the opening and closing remarks) and how should I address him in he letter? should I use さま、さん?