PART OF BUSINESS LETTER

A business letter is more formal than a personal letter. It should have a margin of at least one inch on all four edges. It is always written on 8½"x11" (or metric equivalent) unlined stationery. There are six parts to a business letter.
1. The Heading. This contains the return address (usually two or three lines) with the date on the last line.
Sometimes it may be necessary to include a line after the address and before the date for a phone number, fax number, E-mail address, or something similar.
Often a line is skipped between the address and date. That should always be done if the heading is next to the left margin. (See Business Letter Styles.)
It is not necessary to type the return address if you are using stationery with the return address already imprinted. Always include the date.
2. The Inside Address. This is the address you are sending your letter to. Make it as complete as possible. Include titles and names if you know them.
This is always on the left margin. If an 8½" x 11" paper is folded in thirds to fit in a standard 9" business envelope, the inside address can appear through the window in the envelope.
An inside address also helps the recipient route the letter properly and can help should the envelope be damaged and the address become unreadable.
Skip a line after the heading before the inside address. Skip another line after the inside address before the greeting.
3. The Greeting. Also called the salutation. The greeting in a business letter is always formal. It normally begins with the word "Dear" and always includes the person's last name.
It normally has a title. Use a first name only if the title is unclear--for example, you are writing to someone named "Leslie," but do not know whether the person is male or female. For more on the form of titles, see Titles with Names.
The greeting in a business letter always ends in a colon. (You know you are in trouble if you get a letter from a boyfriend or girlfriend and the greeting ends in a colon--it is not going to be friendly.)
4. The Body. The body is written as text. A business letter is never hand written. Depending on the letter style you choose, paragraphs may be indented. Regardless of format, skip a line between paragraphs.
Skip a line between the greeting and the body. Skip a line between the body and the close.
5. The Complimentary Close. This short, polite closing ends with a comma. It is either at the left margin or its left edge is in the center, depending on the Business Letter Style that you use. It begins at the same column the heading does.
The block style is becoming more widely used because there is no indenting to bother with in the whole letter.
6. The Signature Line. Skip two lines (unless you have unusually wide or narrow lines) and type out the name to be signed. This customarily includes a middle initial, but does not have to. Women may indicate how they wish to be addressed by placing Miss, Mrs., Ms. or similar title in parentheses before their name.
The signature line may include a second line for a title, if appropriate. The term "By direction" in the second line means that a superior is authorizing the signer.
The signature should start directly above the first letter of the signature line in the space between the close and the signature line. Use blue or black ink

Sources :

- http://makalahproposal.blogspot.com/2014/05/contoh-surat-bisnis.html

- http://englishplus.com/grammar/00000149.htm