What is the difference of attention and through below the addressee of the letter?

Attention in a letter typically refers to the specific person or department that the letter is directed to, ensuring that it reaches the correct individual. It is often used in formal correspondence to highlight the intended recipient. In contrast, "through" indicates the pathway or process by which the letter is sent or delivered, often suggesting that it may pass through intermediaries before reaching the final addressee. Essentially, attention specifies who should read the letter, while through relates to the method of delivery.