That's right. When a company, department, group, etc. Send as a whole, without specifying a specific recipient. Of course, you can also use "Yuzhong" on postcards. It should be noted that if the recipient is specified, even the general "responsible person" (responsible person) does not need to add any information after the company organization.

The usage of ~ ~ line is rarely used by ordinary people, such as sending an envelope to others (because the other party doesn't know your address or to reduce the trouble of the other party's reply). In this case, pay attention to the name of the recipient, and finally add "line" to show humility. If you send a letter to others by yourself, you don't need to add "line" to write the address and name of the sender in the lower left corner or on the back of the envelope.

The most common usage of "OK" in daily life is the reply postcard/envelope printed by the company for consumers or customers to send to their own company (mostly postage-free letters at the recipient's own expense) to accept comments from consumers, for example.

Another thing to note is that if you receive an envelope with "OK", the other person shows a humble attitude. Cross out the word "line" with a double line before sending it, and write "line" or "imperial" beside it according to whether the other party is an individual or an organization to show respect for the other party, but don't just put it back.