The three formats of formal letter are block, semi-block, and modified block.
Block format is the simplest and most commonly used format. All of the text is aligned to the left margin and single-spaced. Semi-block format is similar to block format, except that the date, closing, signature, and courtesy title are all indented to the right half of the page. Modified block format is similar to block format, except that the date, closing, signature, and courtesy title are all aligned to the right margin.