Opening Part: The first paragraph of the mail writing must state the introduction of the writer. It also contains the previous correspondence if any. Main Part: This paragraph states the main idea or the reason for writing. It must be clear, concise, complete, and to the point. Concluding Part: It is the conclusion of the business letter. It shows the suggestions or the need of the action. The closing of the letter shows the expectation of the sender from the recipient. Always end your mail by courteous words like thanking you, warm regards, look forward to hearing from your side etc.
For instance, in a typical job application, the problem is that the company or organization needs a position filled, and more importantly they need someone who can do the job well and help the organization achieve its mission (which may be more profits, or it may be to save children in Darfur or to end global warming or to cure cancer). You arouse their interest by telling them that you’re the right person for the position and by promising to help them achieve their mission.