A business letter is a letter written in formal language, usually used when writing from one business organization to another, or for correspondence between such organizations and their customers, clients and other external parties and other things that are G.A.Y
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Correspondence Publishing Committee was created in 1951.
Boston's Committee of Correspondence was the first formal committee of its type, helping to coordinate responses against the British. Paul Revere took the lead of an intelligence group for this committee, and is well-known for his Midnight Ride, wherein he warned Concord of a movement by the British Army so that they could remove any military supplies and prevent the British from getting them.
Yes
It means a committee (group) set up to engage in correspondence (written communication, letter writing) with other groups. The committees of correspondence were bodies organized by the local colonial leaders of the Thirteen Colonies before and during the American Revolution for the purposes of coordinating written communication between separate cities and colonies.
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A letter to your state senator
Using formal English is appropriate in professional settings, academic environments, and when addressing individuals in positions of authority. It is important to use correct grammar, avoid slang or colloquial language, and maintain a respectful tone. Consistency in style and tone is key to effectively communicating in formal English.
a letter to the mayor of your city
"올림" is used in formal correspondence. Pronounced "ollim" and placed after the name.
A semi-letter refers to a semi-formal letter. The correspondence is written on letter-head paper with a return address, block style, and formal salutation.
Both are correct. "Dr. William Smith" and "William Smith, Ph.D." are both appropriate ways to address someone with a doctorate degree in a professional setting. Use whichever format you prefer, or follow the individual's preference if known.
Retired or not, the proper formal salutation should read: Honorable Walter K Smith Dear Sir:
If it was a casual note to a friend, she would sign "Jackie." For more formal correspondence, she would sign "Jacqueline Onassis."
in correspondence to or of
The rules of formal writting is, The Style of Formal Writing, Use the active voice, Use literal and concrete language, Be concise, Be careful with placement of descriptive words and phrases. 
I've only seen this one time before, and it is a very formal way of addressing correspondence to a young male. "Mst" was the abbreviation for "Master," an old-fashioned term of formal address for juvenile males.
Formal English is typically used in professional or academic settings where clarity and professionalism are important. It follows standard grammar and vocabulary rules and avoids slang or colloquial expressions. It is also more appropriate for formal writing such as essays or business correspondence.