What are the rules of spacing for business letters?

In business letters, the standard rules of spacing include using single spacing within paragraphs and double spacing between paragraphs for clarity. The sender's address, date, recipient's address, salutation, body, closing, and signature should each have proper spacing; typically, a double space is used after the recipient's address and the closing. Additionally, leaving a margin of at least one inch on all sides is recommended for a professional appearance.