Length: 3 pages (double-spaced, 1 inch margins, 12 point font).
Picture an actual friend to give yourself a real audience. Write your letter to answer your friend’s questions about plagiarism. If there are cultural differences that you had difficulty with, it is reasonable to assume that your friend would also have questions about them. If you were surprised by the severity of the punishments, then your friend might have questions about that, too.
Structure: Put the date at the top, and begin with a salutation (“Dear Abdullah”). It is not necessary to include a paragraph about the weather at the beginning. Go ahead and jump right into plagiarism. You may sign off with a word that is appropriate to your relationship (“fondly,” “love,” “I miss you,” or something more informal such as “That’s all for now”) and sign your name.
In a formal letter (such as a business letter), you would include your own address under the date, and the name of the addressee and his/her address under that. You can still use the salutation “Dear” but you must use the person’s title and last name: “Dear Professor Mott-Smith” or “Dear Dr. Mott-Smith.” You would sign off with something more formal like “Sincerely,” “With warm regards,” or “Best.” (Personally, I hate “Best” but it’s used a lot in academia.)