the subject line help to tell you reader at a glance what your letter is about. it is typed the left margin. At the paragraph point or centered, two spaces below the salutation. The word subject can be omitted.
your company name, if printed on the letterhead, need not be repeated after the complimentary close, except in legal documents.
Enclosure notation, typed to spaces under the reference symbol, is used when something is sent in the same envelope at the letter. It reminds the writer and his secretary to make sure that enclosure mentioned in the message are mailed with the letter. Meanwhile, this notation also alerts the recipient to check for enclosure. When more than one item is enclosure, number should be indicated.