What should a letter carrier primarily focus on when casing letter mail?

When casing letter mail, a letter carrier should primarily focus on the delivery address. This is because the delivery address is crucial for ensuring that each piece of mail is sorted correctly and delivered to the right location. Accurate casing facilitates efficient mail delivery and helps to reduce the chances of misdelivery, which can occur if addresses are overlooked or not correctly prioritized.

While the physical appearance of the mail, the type of mail being handled, and the volume of mail collected may all be relevant factors in the overall process of handling mail, they do not directly impact the primary task of sorting and casing. Rather, they serve secondary roles; for instance, understanding the type of mail can help in determining handling procedures, and recognizing the volume may influence time management. However, none of these aspects are as critical to the core task of correctly delivering mail as focusing on the delivery address itself.