There are three main formats for business letters: block, modified block, and modified block with indented paragraphs. A business letter consists of a heading with the sender's letterhead and date, an opening with the recipient's address, a salutation, a body with the message, a closing that matches the salutation, a signature, and optional elements like enclosures. Business letters are still used to request or provide information, correct errors, refuse requests, explain procedures, or sell products and services. Personal business letters are written on one's own behalf regarding personal accounts or claims, while social business letters express thanks, congratulations, or sympathy in a business context.