What are the three formats of business letter?

The three main formats of business letters are the block format, the modified block format, and the indented format. In the block format, all text is aligned to the left margin with no indentation. The modified block format has the sender's address and date aligned to the right, while the rest of the letter is left-aligned. The indented format features indented paragraphs, with the sender's address and date typically aligned to the left.