Writing a birthday letter to a friend


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？




I think that it is perfectly fine to use -さん when writing the letter, since
that's what you normally use anyway. If you often speak to him informally,
then you can revert to that style of speech after the opening. I find
[this](http://birthday-techo.com/jyousi-messeji/) to be a good example:

> 例えば・・○○さん、お誕生日おめでとうございます。の後に
>
>   * また今度職場の皆でカラオケに行きましょう！○○さんのあまい歌声をまた聞かせてくださいね。
>
>   * また今度○○さんおすすめのラーメン屋さんに連れていってください！
>
>

>
> といった雰囲気です。

Speaking from experience of writing to professors whom I'm on very friendly
terms with. Hope it's not too late.

