1. Block Format: This is the most common and modern format. All parts of the letter are aligned to the left margin, including the date, inside address, salutation, body paragraphs, closing, and signature.
2. Modified Block Format: This format is similar to the block format, but the date, closing, and signature are aligned to the right margin. This format is slightly more formal than the block format.
3. Semi-Block Format: This format is less common than the other two formats. The date, inside address, and salutation are aligned to the right margin, while the body paragraphs and closing are indented.
All three formats are acceptable, but the block format is generally considered the most professional and modern choice.