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A business letter is usually used when writing from one company to another, or for correspondence between such organizations and their customers, clients and other external parties. The overall style of letter will depend on the relationship between the parties concerned. There are many reasons to write a business letter. It could be to request direct information or action from another party, to order supplies from a supplier, to identify a mistake that was committed, to reply directly to a request, to apologize for a wrong or simply to convey goodwill. Even today, the business letter is still very useful because it produces a permanent record, is confidential, formal and delivers persuasive, well-considered messages.
General Format 
There are two main styles of business letters:
- Full block style: Align all elements on the left margin.
- Modified block style with other elements on the left page margin.
Side, top and bottom margins should be 1 to 1 1/4 inches (the typical default in programs such as Microsoft Word). One-page letters and memos should be vertically centered.
Font Formatting 
No special character or font formatting is used, except for the subject line, which is usually underlined.
Example Template 
[SENDER'S ADDRESS] (optional) [SENDER'S PHONE] (optional) [THE SENDER'S E-MAIL] [DATE] [RECIPIENT W/O PREFIX] [RECIPIENT'S COMPANY] [RECIPIENT'S ADDRESS] (Optional) Attention [DEPARTMENT/PERSON], Dear [RECIPIENT W/ PREFIX]: [First Salutation then Subject in Business letters] [CONTENT.] [CONTENT.] [COMPLIMENTARY CLOSING (Sincerely, Respectfully, Regards, etc.)], [SENDER] [SENDER'S TITLE] Enclosures ([NUMBER OF ENCLOSURES])
Indentation Formats 
Business letters conform to generally one of six indentation formats: Standard, Open, Block, Semi-Block, Modified Block, and Modified Semi-Block. Put simply, "Semi-" means that the first lines of paragraphs are indented; "Modified" means that the sender's address, date, and closing are significantly indented.
In a standard format letter, (1) uses a colon after the salutation, (2) uses a comma after the complimentary closing.
In an open format letter, (1) uses no punctuation after the salutation, (2) uses no punctuation after the complimentary closing.
In a Block format letter, (1) all text is aligned to the left margin, (2) paragraphs are not indented.
In a Semi-Block format letter (1) all text is aligned to the left margin, (2) paragraphs are indented. (3) paragraphs are separated by double or triple spacing.
Modified Block 
In a Modified Block format letter, (1) all text is aligned to the left margin, except for the author's address, date, and closing; and (2) paragraphs are not indented. The author's address, date, and closing begin at the center point.
Modified Semi-Block 
In a Modified Semi-Block format letter, (1) all text is aligned to the left margin, except for the author's address, date, and closing; and (2) paragraphs are indented. The author's address, date, and closing are usually indented in same position
- Guffey, Rhodes and Rogin. Business Communication: Process and Product Third Brief Canadian Edition. Thomson-Nelson, 2010. p.183-214
- Newman & Ober. Business Communication: In Person, In Print, Online. South-Western, 2013. p.503-506