phoenix's answer is not collect...but he has a lot of get-up-and-go:)) keep study;D ”先月、私はあなたにカードを送りましたが、住所がきちんと書けていたか自信がありません。 もし受けとったなら、どうかお知らせください。” it's better;D♥ i prefer this one.

Thank you.　I really should add the relationship I suppose! I am not used to that, but I will try! Now I'm afraid I may have sent an inappropriate message. She hasn't responded to me at all since then, and now I'm worried I said something wrong. :( I get the feeling that I was rude to her, with my last message.... Next time I will include the relationship too! (In this case, she is older and someone who is definitely my sempai in many different ways...) Thank you for the advice! :)

When you ask this kind of question, you should better to write relationships between you and someone. Because translation change who is "someone". Best friend? Friend? Busines? Teacher?.....

先月私は貴方にカードを送信。 アドレスを正しく書いたないと思いますが。