Full block style is a letter format in which all text is justified to the left margin. In block letter style, standard punctuation is placed after salutations and in other headings. Open punctuation, however, refers to a modification of style where all nonessential punctuation is omitted. A few key factors will help you understand block style format and the difference that open punctuation makes.
Semi-block is similar to block but has a more informal appearance. All elements are left-aligned, except for the beginning of each paragraph, which is indented five spaces. Paragraphs are separated by a double line space.