A business letter most often uses block format, in which the letter is single-spaced and left justified, although paragraphs have double spaces separating them. The salutation uses a colon, and the closing has a comma.
Modified block is another correct format for a business letter. The date and closing are centered instead of left justified. Semi-block is not used often but can be correct, depending on the guidelines of the organization. Semi-block adds onto modified block, indenting paragraphs instead of left justifying them.
A business letter begins with the address of the sender, although the letterhead often contains this information. If it does, the letter should skip this part. The sender's address should include the street address, city and ZIP code, but not the sender's name. Next follows the date of writing. The address of the
recipient is one line, or 1 inch, below the date. If, for whatever reason, the letter does not follow block format, the sender's address always needs to be left justified. Only the first letter in the closing is capitalized, and "Enclosures" one line under the closing indicates that the letter includes more material.
A typical font for a business letter, especially to a conservative company or person, is Times New Roman in size 12. Arial is another option.