Subject Line. The subject line gives an advance notice of what the
letter is about to the reader. It is typed one blank line below the salutation.
It may be placed at the left margin, centred, or indented, depending on the
letter style, It should be typed in all capital letters or in underlined upper-and
lower—case letters. The word Subject may be used, but if it is used, it is
followed by a colon However, the subject line is an optional part,
it can be omitted.