Usually, when the inside address doesnt contain the individuals name, attention line is used to name the specific person the letter is addressed to.

通常，当封内地址不包括收件人的姓名时，可使用注意项来标明具体的收件人。

Considered a polite greeting with which a friendly business letter begins, the personal salutation must be appropriate for the first line of the inside address.

友好的商业书信往往以贴切的问候开始，写给个人的信，称呼应与封内地址的礼貌尊称一致。